In a small bowl, whisk together the coconut flour, baking powder, sea salt, and ground cinnamon to break up any lumps and ensure the leavening agent distributes evenly. In a separate small bowl or directly in your mug, mash the banana with a fork until completely smooth with no chunks—this ensures even moisture distribution throughout the cake. Set both mixtures aside.

In your microwave-safe mug, combine the egg whites, melted and slightly cooled coconut oil, almond milk, maple syrup, and vanilla extract. Whisk together until the mixture is smooth and the maple syrup is fully incorporated—this creates an emulsion that helps bind all the ingredients together. I find that letting the coconut oil cool slightly before mixing prevents the egg whites from cooking prematurely.

Add the dry ingredient mixture from Step 1 to the wet ingredients in your mug, stirring gently until just combined—be careful not to overmix, as this can develop gluten and create a tough cake. The batter should be thick but pourable. Fold in the chocolate chips if using, distributing them evenly throughout the batter for pockets of richness in every bite.

Microwave the mug on high power for 2 minutes. The cake will rise significantly and may look slightly wet on top. If the center appears raw or jiggles when you gently shake the mug, heat for an additional 1 minute and check again. I always start with the full 2 minutes, as undercooking is better than overcooking—you can always add time but you can't reverse it!

Let the mug cool for 2-3 minutes before eating—this allows the cake to set slightly and makes it easier to eat straight from the mug. The cake will continue to cook slightly from residual heat during cooling, ensuring a moist interior with a light, fluffy crumb.