01 - Blend cottage cheese, egg, milk, and vanilla extract in a blender or food processor until completely smooth and creamy.
02 - In a 10-12 oz microwave-safe mug, whisk together oat flour, protein powder, baking powder, cinnamon, sweetener, and salt until evenly mixed.
03 - Pour the blended wet mixture into the mug with the dry ingredients. Stir vigorously until fully combined and no lumps remain.
04 - In a small bowl, mix melted butter, cinnamon, and brown sugar until well combined.
05 - Drizzle or dollop the cinnamon mixture into the mug batter. Gently swirl with a knife or skewer to create a marbled effect.
06 - Microwave on high power for 1 minute 30 seconds to 2 minutes, or until the cake is set and springs back lightly when touched. Check at 90 seconds as microwave power varies.
07 - If desired, mix softened cream cheese, milk, vanilla extract, and powdered sugar until smooth and drizzle-able.
08 - Drizzle icing over the warm mug cake and serve immediately for the best texture.