In a stainless steel pan, cook the butter over medium heat until the butter solids at the bottom are an amber brown color (about 10 minutes). Scrape all of the butter into your mixing bowl.

Stir in the espresso grounds and set the bowl aside to cool to room temperature (about 20-30 minutes).

Whisk in the granulated and brown sugar for one minute until well combined.

Whisk in the egg, egg yolk, and vanilla extract.

Fold in the flour, baking soda, salt, and chocolate until just combined.

Scoop the dough onto a parchment-lined baking tray. Chill the tray in the freezer for at least 3-4 hours (overnight for the best flavor and texture).

Preheat the oven to 350°F (180°C). Bake the frozen cookies spaced at least two inches apart for 10-12 minutes or until the edges are golden but the middle is still pale and puffy.

Let the tray cool on a wire cooling rack and enjoy!