Garlic, butter, lemon, and rosemary turn these keto sautéed mushrooms rich and tender in one cast iron skillet with 4.4g net carbs. I cook them at least twice a week because they go with literally everything.
I make these keto sauteed mushrooms more than any other side dish on this site. Not because they’re complicated (they’re the opposite), but because they go from raw to golden brown in about 10 minutes and I haven’t found a single protein they don’t pair with.
The biggest thing I’ve learned making these over the years is that butter timing matters. I used to use butter alone, and it would burn before the mushrooms even started browning. Now I melt the butter with a teaspoon of olive oil right at the start. The oil gives the milk solids more runway before they scorch, so the butter still does all the flavor work without going dark. The lemon juice goes in after the initial browning. If you add acid too early, it slows down the browning process, and you end up with pale, steamed mushrooms instead of the deep golden color you want.
I use a cast iron skillet every time. Cast iron holds heat better than stainless steel, which means the mushrooms sear instead of releasing all their water and stewing. That’s the real secret to getting them crispy on the edges. If your mushrooms always turn out soft and watery, the pan temperature is almost certainly the problem.
The rosemary goes in at the very end, just 30 seconds, because fresh rosemary burns fast. I’ve ruined a batch by adding it too early and ending up with bitter, charred herb bits. Garlic gets the same treatment. Thirty seconds of heat is all they need to release their flavor without going acrid.
One thing that surprises people: 4 cups of raw mushrooms cook down to about 1.5 cups. It looks like a mountain going into the pan, but mushrooms are mostly water. I usually make a double batch so there’s enough for leftovers, because they reheat well in a hot skillet the next day.
The difference between soggy mushrooms and golden, crispy-edged ones comes down to two things: don’t crowd the pan, and let them sit. I spread mine in a single layer with space between each piece and resist the urge to stir for the first 2-3 minutes. That’s when the browning happens. If your skillet isn’t big enough for all of them in one layer, cook in two batches. It takes an extra few minutes, but the result is worth it.
I reach for these as a keto side dish more than almost anything else on my site. They’re the kind of thing I throw together while the main course rests, and they make a plate of cheesy basil zucchini or loaded mashed cauliflower feel like a full spread. Simple prep, big flavor, no filler ingredients.
Swaps and What to Serve Them With
These mushrooms are vegetarian, so they fit a mixed diet holiday table. Swap the butter for olive oil and they are vegan. I use rosemary, but thyme works just as well if that is what you have.
The finished mushrooms, ready to serve with lemon and rosemary on the side.
Sliced or Whole Mushrooms
Slice them or leave them whole, your call. Sliced mushrooms cook faster but need more attention so they do not overcook. If you slice, keep the pieces the same thickness so they cook evenly.
Keto Sautéed Butter and Garlic Mushrooms Ingredients
Step by Step Instructions
1
Heat it up
Heat a large cast iron over medium heat and melt butter with oil. Cook onion until tender then add mushrooms.
2
Cook and add lemon juice
Cook the mushrooms for about 5 minutes until golden brown. Pour in the lemon juice and cook for another 4 minutes.
3
Rosemary and garlic
Add rosemary and garlic in the pan. Stir and cook for 30 seconds. Adjust taste with salt and pepper.
Nutrition
Per serving: 1/4 of recipe
Calories
148
Fat
12.2g
Protein
3.2g
Total carbs
4.9g
Net carbs
4.4g
Nutrition is an estimate calculated from the ingredients listed. Brands vary, so check labels if you track closely.
Frequently Asked Questions
What's the best mushroom variety for sauteing?
I've tested cremini, white button, shiitake, and baby bella in this recipe. Cremini are my go-to because they have a meatier texture and deeper flavor than white button. Shiitake are great if you want something more earthy, but I remove the stems because they're too tough. Baby bellas are just mature cremini, so they work the same way. For a keto side dish, any of these keep the carbs low. I'd skip portobello caps here though. They're better stuffed or grilled whole.
How do I store and reheat leftover sauteed mushrooms?
I make a double batch on Sunday and use them throughout the week. They keep in the fridge for 3-4 days in a sealed container. To freeze, I spread them flat on a sheet pan first, then transfer to a bag. They keep about 3 months, though they lose that crispy seared edge after thawing, so frozen ones are best stirred into stir-fries or soups. Either way I reheat in a hot skillet with a tiny bit of butter, never the microwave. The microwave makes them rubbery. A minute or two in a hot pan and they crisp right back up.
What can I substitute for butter to make this dairy-free?
I've made these with ghee and with avocado oil. Ghee gives you that buttery richness without the milk solids, so it's my first choice for dairy-free. Avocado oil works too but the flavor is more neutral. I'd skip coconut oil here because it adds a sweetness that clashes with the garlic and rosemary. Whatever you use, the technique stays the same.
Can I add wine or broth to deglaze the pan?
I do this sometimes when I want a little sauce at the bottom. A splash of dry white wine right after the mushrooms brown creates these incredible fond bits. Let it cook off for about 30 seconds before adding the garlic. Bone broth works too if you skip the wine. I've used both, and the wine version has a sharper, more complex flavor. Just keep it to 2 tablespoons or the mushrooms will start steaming.
Use Kerrygold here. The butter flavor carries in a way cheaper brands don’t, and with the lemon and rosemary it actually matters. Garlic mushrooms in cast iron used to mean a steakhouse appetizer I ordered on autopilot. This is that, except I can have it twice a week.
Tamika, mostly yes. The oil gives the butter a little more runway before the milk solids start to scorch. Butter alone in a really hot cast iron pan goes dark fast. I keep the olive oil to just a teaspoon so butter’s still doing the flavor work. Mushrooms dump so much water when they first hit the pan that it helps slow things down anyway. Crowding is actually the bigger problem.
Annie, nobody else puts lemon juice in a garlic mushroom recipe, and somehow that’s the whole point. Most versions just layer butter and garlic and stop there. Gets heavy by bite three. The acid keeps it from sitting flat, and I could never figure out what it was doing with the rosemary until now. Four stars only because my cast iron runs hot and the mushroom timing needs more attention than the recipe lets on, but that’s a me problem.
4.4 net carbs felt too low for something that tastes this rich, so I finally made it last week. I went in skeptical about the lemon juice (mushrooms and acid felt like a weird combo to me) but it does something to the butter sauce that I can’t fully explain, just softens the richness without going sour. Cast iron made the difference, mine went golden in five minutes and never steamed. Four stars only because the rosemary can get piney if you let it go too long, I pull it a minute early now, but this is way better than anything I was doing before with just olive oil and salt.
My son asked for ‘the garlic mushrooms’ again the next morning. First time a side dish made the breakfast list. I think the lemon is what keeps them from sitting too heavy.
Fresh makes a difference but dried works fine. I’d cut it to about 1/3 teaspoon since dried is way more concentrated, and crush it between your fingers first to get the oils going. The main thing you lose is texture. Fresh leaves get almost crispy in the butter.
Tried this with oyster mushrooms instead of whole white and they got almost lacey at the edges when they browned. Kept the five garlic cloves and the lemon but cut the cook time to about three minutes since they’re so much thinner. Worth it if you can find them.
Oyster mushrooms weren’t on my test list for this one, but lacey edges in a cast iron is exactly what you want from that mushroom. Three minutes sounds right. Push it past that and they’ll fall apart.
I don’t usually make side dishes from scratch but saw this and gave it a try. The garlic and lemon together once everything hits that hot cast iron is something else. Do you think dried rosemary would work if I can’t find fresh?
Added a splash of dry white wine right before the lemon juice and the sauce that formed in the pan was something else. Still getting that rosemary and garlic hit but now there’s this whole other layer underneath it. Four stars because I haven’t made it as written yet, but this version is going on repeat.
If your mushrooms keep steaming instead of browning, stop stirring them (I was moving mine constantly and the moment I left them alone for a few minutes in the cast iron they finally got that golden color). Also swapped the regular onion for shallots and the sweetness goes so much better with the lemon.
The shallot swap is worth it. The sweetness works better with the lemon and butter than regular onion does. And yeah, once they hit the pan just walk away.
I went off plan for about two months over the holidays and getting back to keto always feels like starting from scratch. Made this last week on a Sunday when I needed a win, and the moment the rosemary hit the cast iron, the whole kitchen smelled like a bistro I used to love before I ever knew what net carbs were. That smell alone was worth it. The lemon and butter here is not subtle, which I mean as a compliment. I’ve made a lot of ‘lighter’ mushroom sides over the years that tasted like substitutions, and this one doesn’t feel like anything was traded away. There’s a specific golden you get on mushrooms in cast iron around minute five or six that just doesn’t happen in a regular pan, and once you see it you know. Four stars because I’d push the garlic even harder next time, but this is already going into the spring rotation.
Seven or eight cloves if you want more garlic. Five is my baseline but it handles more without going bitter. And yeah, that minute-five color is exactly why I stopped using a regular pan for mushrooms.
Good recipe overall, and the cast iron is the right call for getting that browning on the mushrooms. My one note: 5 minutes wasn’t quite enough to drive off the moisture before the garlic went in, so mine turned a little bitter from the garlic hitting a wet pan. An extra 2-3 minutes at medium-high before adding the rosemary and garlic fixed it completely.
Good catch. Moisture varies a lot batch to batch, so 5 minutes is really the floor. Cast iron holds heat well enough that 7-8 minutes before the garlic usually gets you there without the bitterness.
