Add butter to your mug. Microwave until melted. Stir vanilla extract, milk and sugar into the butter. Add flour, baking powder and salt and stir until just combined.
Microwave mug cake 1.5 to 2 minutes. Be careful removing the mug from the microwave as it may be hot.
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Notes
Note: I used 2% milk when testing the recipe but you can use whatever milk you have on hand whether it's whole, skim or almond milk.A key to keeping the texture super light and fluffy is mixing it just until it comes together. Any extra stirring could make it tough or gummy.Topping Ideas for Vanilla Cake: