Preheat the oven to 350°F (175°C). Line a muffin tin with 6 liners.
In a mixing bowl, whisk together the almond flour, coconut flour, baking powder, salt, and xanthan gum.
In another bowl, combine the melted butter, eggs, sour cream, and erythritol until smooth.
Gradually fold the dry ingredients into the wet ingredients until a thick batter forms.
Scoop the batter evenly into the prepared muffin liners.
Bake for 18-20 minutes or until the tops are golden and a toothpick inserted comes out clean.
Allow to cool for 10 minutes before serving.