Preheat the oven to 350°F and line a cookie sheet with a silicone baking mat or parchment paper.
Using a stand mixer with a paddle attachment, or hand mixer, cream the room temperature brown butter, brown sugar, and granulated sugar until smooth and creamy.
Add in the egg and vanilla extract and beat until light, fluffy, and pale in color. This should take 2-4 minutes which seems like a long time, but you'll see a huge difference in the texture afterwards.
Add in the flour, baking soda, cornstarch, and salt and mix until thoroughly combined. The dough should be soft but not very sticky.
Gently fold in the mini chocolate chip cookies.
Scoop the dough into small 1 teaspoon sized balls and then press a few extra mini chocolate chips on top!
Arrange the cookie dough balls 1-2 inches apart on a lined baking sheet.Note: there is typically no need to chill the cookies before baking. However, if your kitchen is very warm and the dough is starting to melt a bit, pop the tray in the fridge for 10 minutes before baking.
Bake at 350°F for 6-8 minutes or until the cookies are just set on top. (They might look a bit under baked, but the cookies will continue to bake as they cool).
Let the cookies cool on the baking sheet for 10 minutes, then remove and let them finish cooling on a wire rack.
Store cookies in an airtight container at room temperature for up 5 days.
Notes
To make brown butter, melt unsalted butter over medium heat, stirring frequently. Watch closely for the butter to develop brown specs and a nutty aroma. Once you start seeing brown specs, let cook for just a few seconds longer (watch very carefully or it will burn). Remove from the heat and pour into a small bowl so that it doesn't continue to cook . Set aside and let cool for about 20 minutes in the fridge until soft and pliable. Note: For every ½ cup (1 stick or 113g), you'll lose about 1 tablespoon (14g) to evaporation while cooking. So you can either add in an extra 1 tablespoon before browning, or if you're browning big batches, just make up the weight difference in your recipe with regular unsalted butter if needed.Freeze pre-rolled cookie dough balls in the freezer for up to 6 months.