'Preheat the oven to 350℉/176℃ and line 2 baking trays with parchment paper and set aside.
In a pot over medium-high heat, add the butter. Allow it to melt, then it'll begin to sizzle and foam. Continue stirring for 2-3 minutes until brown specks form on the bottom of the pot and the aroma of browned butter arrives. This should take 3-5 minutes total. Transfer to a heat-safe glass cup to cool as you prep the rest of the ingredients. The butter should sit and cool for 20 minutes before using.
3/4 cups unsalted butter
In a bowl, add the flour, baking soda, baking powder, cornstarch, cinnamon, and salt. Stir to combine and set aside.
2 cups all-purpose flour, 1 tsp baking soda, 1/2 tsp baking powder, 1 tbsp cornstarch, 1/4 tsp cinnamon, 1/4 tsp salt
In another bowl, add the brown butter (it can be lukewarm, but not hot), brown sugar, white sugar, and vanilla. Whisk well and combine.
3/4 cups unsalted butter, 2/3 cups dark brown sugar, 1/4 cup white sugar, 1 tbsp vanilla
Whisk in egg, egg yolk, and sour cream.
1 large egg, 1 large egg yolk, 2 tbsp sour cream
Combine the dry and wet ingredients together until almost completely combined, then mix in the chocolate chips. Stir just until the flour streaks disappear - do not over-mix!
3/4 cups semi-sweet chocolate chips
Scoop 6 cookies per tray, spacing them evenly from one another (about 2 tbsp per cookie). Add extra chocolate chips on top if desired.
Bake for 10-12 minutes, or until the edges are a light golden brown and the middles are puffy. Allow to cool, and enjoy!