In a microwave-safe mug, combine 4 tablespoons of all-purpose flour, 2 tablespoons of sugar, 1/4 teaspoon of baking powder, and a pinch of salt. Stir these dry ingredients together until well blended.

Add 2 tablespoons of Biscoff cookie butter, 3 tablespoons of milk, 1 tablespoon of vegetable oil, and a splash of vanilla extract into the mug. Mix until the batter is smooth.

Place the mug in the microwave and cook on high for 1 to 1.5 minutes. Keep an eye on it as it cooks; the cake should look set but soft to the touch.

After microwaving, carefully remove the mug and allow the cake to cool for 1 minute before enjoying.