Preheat the oven to 350F and generously grease a 24 cup mini muffin pan. In a large bowl, whisk together the almond flour, coconut flour, 1/3 cup allulose, baking powder, salt and nutmeg.----------------
In a separate bowl, whisk the eggs, 1/4 cup melted butter, sour cream and vanilla until smooth. Pour into the dry ingredients and stir until you have a thick, scoopable batter.----------------
Scoop about 1 tablespoon of batter into each of 18 muffin cups and round the tops with damp fingers. Bake for 12 to 14 minutes until puffed and golden on the edges.----------------
While they bake, melt 1/4 cup butter in a small skillet over medium heat and keep cooking, swirling, until it turns golden brown with a nutty smell, about 4 minutes. Pour into a shallow bowl.----------------
In another shallow bowl, mix 1/3 cup allulose with the cinnamon.----------------
Let the donut holes cool in the pan for 3 minutes, then remove them while still warm. Roll each one in the brown butter, then immediately in the cinnamon sugar until fully coated.----------------
Place on a wire rack for 5 minutes so the coating sets. Serve warm, or store in an airtight container at room temperature for up to 2 days.