In a medium bowl or large mug, mash the ripe banana thoroughly until mostly smooth with just a few small lumps remaining—this creates a creamy base. Crack the egg directly into the bowl and whisk vigorously until the banana and egg are fully combined and slightly fluffy, about 30 seconds. This whisking aerates the mixture and helps create a lighter crumb structure. Stir in the vanilla extract until evenly distributed.

Add the full-fat cottage cheese to the wet base from Step 1 and stir until mostly smooth—a few small curds are fine and add nice texture. Gently fold in the rolled oats using a spatula, stirring just until no dry oats remain and the batter comes together. I find that overmixing at this stage can make the cake dense, so aim for a loose, chunky batter rather than completely uniform.

Stir the chocolate chips into the batter from Step 2 until evenly distributed. Pour the entire batter into a microwave-safe mug or ramekin (8-10 oz capacity works best). For microwave cooking: heat for 1½ to 2 minutes on high power—start checking at 1½ minutes, as the cake will continue to set as it cools slightly. For air fryer cooking: transfer to a small oven-safe ramekin or mug-shaped baking vessel and cook at 390°F (200°C) for 8–10 minutes until a toothpick inserted in the center comes out mostly clean. I prefer the air fryer method because it creates a slightly firmer, more cake-like texture compared to the microwave version.