Lightly grease a microwave-safe mug with cooking spray or oil.
In the mug, whisk together the almond flour, cocoa powder, baking powder, and salt until well combined.
Add the honey or maple syrup, unsweetened applesauce, milk, and vanilla extract to the mug. Stir until smooth and no lumps remain. Add a chocolate square or chocolate chips.
Microwave the mug cake on high for 60-90 seconds, or until the cake has risen and is set in the middle.