In a 12-ounce microwave-safe ceramic mug, combine the flour, sugar, baking powder, and sea salt. Use a fork to whisk these together until no clumps remain. This ensures the leavening agent is evenly distributed, preventing your high-protein vegetarian snack from having a lumpy or uneven texture.
Add the milk, melted butter (or oil), and vanilla extract directly into the mug. The vanilla is the key to that professional, bakery-style aroma. If you prefer a richer flavor, using whole milk provides the necessary fats to keep the mug cake moist during the rapid microwave cooking process.
Mix with a fork until the batter is smooth, making sure to scrape the bottom corners of the mug where dry flour often hides. If you are adding rainbow sprinkles, fold them in gently now. Avoid over-mixing at this stage, as too much agitation can make the cake rubbery instead of fluffy.
Place the mug in the center of the microwave and cook on high for 70 to 90 seconds. The cake will rise significantly before settling. It is done when the top is dry to the touch and the edges pull away slightly from the mug. Every microwave varies, so start with the lower time first.
Allow the mug cake to rest for a full 2 minutes before eating. This is a top-notch cooling step that allows the internal steam to finish the cooking process and lets the delicate vanilla sponge set firmly. This patience ensures a perfect, tender crumb rather than a gummy center.
Finish your cake with a dollop of Greek yogurt, whipped cream, or extra sprinkles. The addition of Greek yogurt is a smart high-protein vegetarian choice that balances the sweetness and adds a creamy, professional finish to your single-serving dessert.
