Preheat oven to 375°F (190°C) and grease a 24-cup mini muffin tin with butter or non-stick spray.

In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.

In a separate medium bowl, whisk together the milk, egg, melted butter, and vanilla extract.

Pour the wet ingredients into the dry ingredients and stir until just combined; do not overmix.

Distribute the batter evenly into the 24 mini muffin cups, filling each approximately 3/4 full.

Top each cup with optional chocolate chips or blueberries if desired.

Bake for 12 to 15 minutes, or until the poppers are golden brown and a toothpick inserted into the center comes out clean.

Allow to cool in the pan for 2 minutes before transferring to a wire rack or serving plate.