Step 1

Preheat oven to 375°F. Line a sheet pan with parchment paper.

Step 2

In a small saucepan set over medium heat, melt the butter. Continue to cook the butter until it turns golden brown, stirring frequently, about 3 minutes. Remove from heat and let cool for a few minutes.

Step 3

Pour browned butter into a large bowl and add the sugar, brown sugar, and vanilla. Stir with a wooden spoon until combined. Add the egg and egg yolk, stirring for 30 seconds after each. Let batter rest for about 5 minutes, then stir vigorously for about 30 second. Batter should lighten in texture and color.

Step 4

In a separate bowl, combine the flour, baking soda, and salt. Add to the cookie batter all at once and stir until no streaks of flour remain.

Step 5

Drop dough by rounded tablespoon onto the prepared sheet pan. Bake until cookies turn golden around the edges but centers aren't completely set, about 9-11 minutes. Let cool 5 minutes on the pan, then transfer to a wire rack to cool completely.