1. To a 9-inch bundt cake pan, coat the inside with a thin layer of butter. Using a mesh strainer, dust a small amount of oat fiber over the butter to coat. Set aside. Preheat oven to 350 degrees.
2. To a large bowl, cream together softened butter and sweetener. Mix with an electric mixer until fluffy and smooth (2-3 minutes). Add eggs one at a time. Then stir in vanilla. Set aside.
3. In a medium bowl, add 2 cups almond flour, 1/4 cup oat fiber, 1 teaspoon baking powder, 1/2 teaspoon salt and pumpkin pie spice. Mix until combined.