Add the butter and stout to a pan over medium heat. Allow to melt and become foamy, stirring frequently.

After about ten minutes the foam will subside and the liquid will become more translucent and you will be able to see the bottom of the pan and small bits on the bottom. Whisk continuously until it smells nutty and the bits have browned.

Remove from heat and add to the bowl of a stand mixer. Allow to sit until cool to the touch, about 30 minutes (if you don’t allow the butter to cool it will melt the sugar and your cookies will turn out flat and greasy).

Preheat the oven to 400°F.

Add the brown sugar and white sugar to the stand mixer with the cooled brown butter, beat until well combined.

One at a time add the eggs, yolk and vanilla allowing to beat well between additions. Beat on high speed until the mixture is creamy and resemble frosting.

Bake for 9 minutes or until the cookies are golden brown at the edges and the center has puffed. Pull the parchment onto the counter to allow the cookies to cool.