01 - Combine cottage cheese, egg, milk, and vanilla extract in a blender or food processor. Blend until completely smooth and creamy, approximately 30-45 seconds.
02 - In a 10-12 oz microwave-safe mug, whisk together oat flour, protein powder, baking powder, cinnamon, granulated sweetener, and salt until evenly distributed.
03 - Pour the blended wet mixture into the mug with dry ingredients. Stir thoroughly until no dry pockets remain and batter is uniform in consistency.
04 - In a small bowl, mix melted butter, cinnamon, and brown sugar until combined. Drizzle mixture over batter and gently swirl through using a knife or skewer to create marbled effect.
05 - Cook on high power for 1 minute 30 seconds to 2 minutes. Cake is done when set and springs back lightly when touched (microwave wattage varies; check at 90 seconds).
06 - If desired, whisk together softened cream cheese, milk, vanilla extract, and powdered sugar until smooth and drizzle-friendly.
07 - Drizzle icing over warm mug cake and serve immediately for optimal texture and flavor.