Preheat your oven to 175°C (350°F).
Place the 170 grams of salted butter in a small saucepan over medium heat. Stir occasionally, scraping the bottom, until it turns a deep amber color and releases a nutty aroma. Remove from the heat into a heatproof bowl and let it cool for ten minutes
Measure both sugars into a medium bowl. Once the brown butter has cooled slightly, add it to the bowl and mix until combined.
Fold in the vanilla paste, egg and egg yolk until fully incorporated. The batter should thicken a little and feel creamy
Grab a second bowl and divide the dough into two equal portions, about 225 grams each. To the first portion, gently fold in the flour for the chocolate-chipless dough, along with ¼ teaspoon baking soda and ¼ teaspoon salt
To the second portion, fold in the flour, 25 grams of cocoa powder, ¼ teaspoon baking soda, ¼ teaspoon salt, ½ teaspoon espresso powder, and ⅛ teaspoon cinnamon. Mix just until combined, being careful not to overwork the dough
Shape the cookies by scooping out 30-gram portions of dough. For a subtle marbled effect, alternate the two doughs in each cookie, or for an easier method, simply press half of each dough together. Arrange the cookies on a lined baking sheet, leaving some space between each
Bake for 10–12 minutes, until the edges are set and lightly browned. Around the 6-minute mark, carefully remove the pan, give it a quick tap on the counter, then return it to the oven, rotating the pan so the cookies bake evenly
Let the cookies rest on the pan for 10 minutes before transferring to a wire rack to cool completely
And you're done!