Melt butter in a microwave-safe bowl, then add the yogurt, egg, and vanilla extract. Mix well to combine.
Add the dry ingredients to the wet by adding almond flour, baking powder, and allulose. Stir to combine, trying to get rid of any lumps.
If needed, pour batter into a mug or ramekin that leaves some space at the top.
Sprinkle blueberries into the batter and fold them in loosely.
Microwave for 60-90 seconds. It should be cooked on the outside and moist in the middle. If still uncooked in the middle, microwave in 10 second increments. Serve hot and enjoy!
Notes
This makes a total of 1 serving of Keto 90-second Blueberry Muffin. The serving comes out to be 403 calories, 32.2g fats, 7.4g net carbs, and 15.6g protein.