To brown butter, heat unsalted butter in a light color saucepan over medium heat. Once the butter melts, it will become foamy. When the foam subsides, you will see clear bubbles, start whisking continuously at this point to keep the milk solids from burning. When the butter is caramel in color and smells nutty, turn off the heat and set aside to cool. This will take around 8 - 9 minutes.

Beat together cool brown butter and sour cream until well combined.

Sift flour, cornstarch, and ½ cup of powdered sugar together in a small mixing bowl using a fine mesh seive. Add salt and mix with a whisk to distribute evenly.

Add the flour mixture to the brown butter mixture and mix with a spatula to form a dough. Refrigerate the dough for 1 hour.

Divide cookie dough with a medium cookie scoop (1 ½ tablespoons) or pinch off 1 oz portions using a scale. Roll into balls and place on a lined baking sheet about 2” apart.

Preheat the oven to 350°F.

Bake, one baking sheet at a time if they don’t all fit on 1 baking sheet, for 15-16 mins until the bottom edges are golden brown.

Remove the baking sheet from the oven and place it on a cooling rack. Let cookies cool completely on the baking sheet.

Roll cookies in powdered sugar generously.