Preheat the oven to 350°F / 175°C. Line a muffin tin with 6 parchment liners.
Make the brown butter. Add the butter to a small saucepan set over medium heat. Stir the butter occasionally until it turns amber in color and develops little brown specks.
Transfer the brown butter to a medium sized mixing bowl and set it in the freezer in 5 minute intervals, stirring between each, until the brown butter thickens.
Brown Butter Cupcakes
Add the flour, baking powder, salt, sugar, and 65g of the room temperature brown butter to a medium sized mixing bowl. Use a hand mixer or a stand mixer fitted with the paddle attachment to beat the mixture together until the butter has combined with the dry ingredients.
Add in the egg white, vanilla, sour cream and milk and whisk just until a cohesive batter has formed.
Distribute the batter evenly between the six liners. Bake for 15-18 min., or until a toothpick inserted in the center of the cupcakes comes out clean.
Cookie Dough Buttercream
Place the flour in a microwave safe bowl and heat it in 30-second intervals until it reaches 165°F / 74°C.
Add the brown sugar, salt. and remaining room temperature brown butter to a medium sized mixing bowl. Beat the mixture on medium-high speed for 4 minutes.
Add in the powdered sugar and heat treated flour, and beat until combined. Then, beat in the vanilla and 1 tbsp. heavy cream. If desired, add in another tbsp. of heavy cream to reached your desired consistency.
Once the cupcakes have cooled to room temperature, pipe the cookie dough buttercream onto them and garnish with chocolate chips and mini cookies. Serve and enjoy!