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.
02 - Add flour, sugar, lemon zest, baking powder, and salt. Mix until just combined, scraping down the sides of the mug.
03 - Microwave on high for 1 minute 30 seconds to 2 minutes, or until the cake has risen and the center is set.
04 - Let cool for 2-3 minutes before serving. Enjoy directly from the mug, optionally garnished with powdered sugar, extra lemon zest, or yogurt.