Use a microwave-safe mug or ramekin for this recipe. Grease the inside with a little butter or oil to prevent sticking.
In a small bowl, whisk together almond flour, coconut flour, baking powder, and a pinch of salt.
Add the melted butter or coconut oil to the dry ingredients and mix well.
Crack the egg into the mixture and whisk until the batter is well combined. Make sure there are no lumps.
Pour the batter into the greased mug.
Microwave the mug on high for about 90 seconds. Cooking times may vary based on your microwave, so keep an eye on it. The bread should rise and firm up.
Allow the bread to cool for a minute or two before removing it from the mug. Once cooled slightly, you can tip it out onto a plate or cutting board. Slice it as desired.