01 - Combine cottage cheese, egg, milk, and vanilla extract in a blender or food processor. Blend until completely smooth and creamy.
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 thoroughly until fully combined and no dry pockets remain.
04 - In a small bowl, mix melted butter, cinnamon, and brown sugar until uniform. Drizzle or dollop this mixture over the batter in the mug.
05 - Gently drag a knife or skewer through the batter in a circular motion to create a marbleized cinnamon swirl pattern.
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, combine softened cream cheese, milk, vanilla extract, and powdered sugar in a small bowl. Mix until smooth and drizzle-consistency.
08 - Drizzle the icing over the warm mug cake. Serve immediately while warm for optimal texture.