Using a large spoon, scoop out the browned butter and into the bowl of a stand mixer with the paddle attachment affixed.
Add brown sugar and granulated sugar.
¾ cup dark brown sugar, ½ cup granulated sugar
Turn mixer on low for a few seconds, then gradually increase speed to medium-high, mixing for about 3-4 minutes until well incorporated and fluffy.
Once the butter sugar mixture is light, fluffy and starts to stick to the sides of the bowl, it’s ready for the next step.
Turn mixer to low and add egg yolks, vanilla, and sour cream.
3 large egg yolks, 1 ½ tablespoons vanilla extract, 2 tablespoons sour cream
Mix on medium for about 30 seconds until well incorporated, stopping to scrape down the sides and bottom with a rubber spatula, as needed.
With mixer off, add in both flours, salt, baking soda and baking powder.
1 cup cake flour, 1 ½ cups all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, 1 teaspoon kosher salt
Turn mixer on low and stir until just combined. Do not over mix.
Add in chopped chocolate and stir on low just until chocolate is evenly incorporated.
Portion dough into 2 tablespoon size balls, rolling between your palms to ensure a smooth ball.
Place about 2 inches apart on prepared baking sheets.
Stick more chocolate pieces to top of each ball, if desired (this helps create those pools of melty chocolate on top of the cookies). Sprinkle cookie dough with flaky salt
flaky sea salt
Bake in preheated oven for 4-5 minutes if using convection (7-8 minutes in conventional oven) then rotate baking trays and bake for another 4-5 minutes for convection (7-8 minutes for conventional).
Allow to cool for 15 minutes on trays then transfer to wire racks.