Preheat your oven to 350°F (175°C). Line a 24-cup mini muffin pan with mini paper liners, or use a clean, well-seasoned nonstick pan if you prefer muffins without liners. Make sure the muffin cavities are clean and dry before adding the batter. This helps the muffins release more easily after baking.

In a large mixing bowl, add the all-purpose flour, granulated sugar, baking powder, and fine salt. Whisk until everything is evenly distributed and no visible pockets of baking powder remain. The mixture should look uniform, loose, and slightly powdery. Breaking up small flour lumps at this stage helps prevent excessive stirring later.

In a separate medium bowl, whisk the egg until the yolk and white are fully combined. Add the whole milk, melted and cooled butter, and vanilla extract. Whisk until the mixture looks mostly smooth and evenly blended. A few tiny droplets of butter may remain visible, especially if the milk is cooler than the butter. This is normal.

Pour the wet mixture into the bowl of dry ingredients. Using a silicone spatula, gently fold the ingredients together until the flour is just incorporated. The batter should be thick, soft, and scoopable rather than thin or runny. A few small lumps are completely normal. Avoid stirring until perfectly smooth, as overmixing can develop too much gluten and produce tough muffins. If you notice a few dry streaks, fold the batter gently until they disappear.

Add 1/3 cup (about 57 g) mini semisweet chocolate chips to the batter. Fold gently until the chocolate chips are distributed throughout. The batter should remain thick enough to hold the chips in place without them immediately sinking to the bottom. Avoid excessive mixing at this stage.

Divide the batter evenly among the 24 prepared mini muffin cavities, filling each approximately three-quarters full. A small cookie scoop makes portioning easier and helps keep the muffins similar in size. Do not pack the batter down. Let it settle naturally into the cavities. The surface may look slightly uneven, which is normal for muffin batter.

Sprinkle the reserved 2 tablespoons plus 2 teaspoons (about 28 g) mini semisweet chocolate chips over the tops of the unbaked muffins. Press them very lightly into the surface so they stay in place as the batter rises. Keeping some chocolate chips on top makes the finished muffins look more appealing and gives each muffin a visible chocolate topping.

Place the muffin pan on the center rack of the preheated 350°F (175°C) oven. Bake for approximately 12 minutes, until the tops are set and the edges are lightly golden. The muffins should rise into small, gently rounded domes. To check for doneness, insert a toothpick into the center of a muffin, avoiding a visible chocolate chip. It should come out clean or with a few moist crumbs, but no wet batter. If the centers still appear wet, continue baking briefly and check again. Oven performance and individual pan dimensions can affect the exact finish.

Remove the pan from the oven and allow the muffins to cool in the pan for 5 minutes. The muffins will continue to firm up slightly as they cool, making them easier to remove without tearing. Carefully transfer them to a wire rack and let them cool for another 5 minutes before serving. The tops should feel lightly springy, and the interiors should remain soft and tender.