In a large mixing bowl, combine the melted unsalted butter and granulated sugar, whisking them together until well mixed. Then, add in the sour cream, whole milk, room temperature eggs, and vanilla extract. Continue whisking until the mixture is fully combined and smooth, which should take about 2-3 minutes.

Next, gently fold in the mashed ripe bananas into the wet mixture, aiming for a smooth consistency without any lumps. This step should only take about 1-2 minutes.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and sea salt. Gradually add the dry ingredients to the banana mixture, stirring gently until just combined; this should take about 1-2 minutes.

Now it's time to fold in your mini semi-sweet chocolate chips into the batter. Use a spatula to carefully incorporate the chips.

Cover the bowl tightly with plastic wrap and let the banana muffin batter rest at room temperature for 1 hour.

Preheat your oven to 350°F (175°C). While it heats up, line your muffin pans with paper liners.

Using a scoop or spoon, fill each muffin cup to the top with the muffin batter, then sprinkle the extra mini chocolate chips on top.

Slide your filled muffin pans into the preheated oven and bake for 22-24 minutes. To check for doneness, insert a toothpick into the center of a muffin.

Once baked, allow the muffins to cool in the pan for about 10 minutes, then transfer them to a wire rack to cool completely.