3. Transfer the bloomed gelatin to a larger bowl and pour in 1 cup boiling water. Stir to dissolve gelatin. Add marshmallows. Heat in the microwave at 30 second intervals, stirring in between, until marshmallows have dissolved. Can use a stovetop as well. Stir in heavy cream. Let cool to room temperature before pouring on the red layer to avoid melting the red layer. Refrigerate for 1 hour or until set.