Preheat oven to 350 degrees. Line cupcake pan with paper liners.
Whisk almond flour, flaxseed meal, coconut flour, baking powder, baking soda, xanthan gum and saltin medium bowl until thoroughly combined.
In medium saucepan, heat butter, sour cream, cocoa powder and espresso powder over low heat until melted and combined, stir constatnly. Transfeer to mixing bowl.
Add sweetener to cocoa mixture and beat until fluffy.
Add eggs, one at a time, beating well after each addition.
Add the flour mixture and beat slowly until completely blended.
Divide the batter into prepared cupcake pan. Fill each paper cupcake liner no more than 2/3 full.
Bake for 14-17 minutes, depending on the size of the cupcake liner, or until a toothpick inserted comes out clean. TAKE CARE NOT TO OVER-BAKE.
Allow to cool completely befor frosting.