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 ounce microwave-safe mug, whisk together oat flour, protein powder, baking powder, cinnamon, sweetener, and salt until evenly distributed.
03 - Pour the blended wet mixture into the mug with dry ingredients. Stir vigorously with a spoon until no dry pockets remain and batter is uniform.
04 - In a small bowl, stir together melted butter, cinnamon, and brown sugar until combined. Drizzle over batter in mug and gently swirl through with a knife or skewer to create marbled effect.
05 - Place mug in microwave and cook on high power for 1 minute 30 seconds to 2 minutes. Cake is done when set and springs back lightly when touched—begin checking at 90 seconds as microwave power varies.
06 - While cake cools slightly, whisk softened cream cheese with milk, vanilla extract, and powdered sugar until smooth and drizzle-consistency.
07 - Drizzle icing over warm mug cake if desired. Serve immediately while warm for optimal texture and flavor.