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 completely smooth.
02 - Add flour, sugar, lemon zest, baking powder, and salt to the mug. Mix until just combined, scraping down the sides to incorporate any dry pockets.
03 - Microwave on high power for 1 minute 30 seconds to 2 minutes, until the cake has risen and the center is set.
04 - Let cool for 2-3 minutes before enjoying directly from the mug. Optionally garnish with powdered sugar, extra lemon zest, or a spoonful of yogurt.