Prep the pan and oven. Heat the oven to 375°F (190°C). Line a 24-cup mini muffin tin with liners or lightly grease with cooking spray.
Mix dry ingredients. In a medium bowl, whisk flour, granulated sugar, brown sugar, baking powder, baking soda, and salt until well combined.
Whisk wet ingredients. In a separate bowl or large measuring cup, whisk milk, egg, oil, and vanilla. If using yogurt or sour cream, whisk it in now.
Combine gently. Pour wet ingredients into the dry.
Stir with a spatula just until the flour disappears. The batter should be thick and slightly lumpy. Do not overmix.
Fold in chips. Add mini chocolate chips and fold just to distribute.
Fill the cups. Spoon batter into the mini muffin cups, filling each about 3/4 full. Sprinkle a few extra chips on top for a bakery look.
Bake. Bake 9–11 minutes until the tops are set and a toothpick comes out with a few moist crumbs. Do not overbake or they’ll dry out fast.
Cool briefly. Let muffins rest in the pan for 3 minutes, then transfer to a wire rack to cool.
Serve warm or at room temperature.