Whisk egg with coconut milk. Stir in flours, coconut flakes, baking powder, and apple cider vinegar and mix very well (chestnut flour tends to clump). Pour into a large mug or small ramekin. Microwave on HIGH (100 percent power) for 90 seconds or so. Cool and enjoy!
Recipe by Create Delicious at https://createdelicious.com/chestnut-flour-muffin-in-a-mug/