01 - In a microwave-safe mug (at least 12 oz capacity), whisk together cottage cheese, egg, milk, melted butter, lemon juice, and vanilla extract until smooth and fully incorporated.
02 - Add flour, sugar, lemon zest, baking powder, and salt to the mug. Mix until just combined, ensuring to scrape down the sides of the mug to incorporate any dry pockets.
03 - Microwave on high power for 1 minute 30 seconds to 2 minutes, or until the cake has risen and the center is completely set.
04 - Allow the mug cake to cool for 2-3 minutes before enjoying. Optionally garnish with powdered sugar, additional lemon zest, or a dollop of yogurt.