Brown 2 sticks of butter (1 cup) to a deep golden brown. Remove butter to a container and refrigerate until just barely solidified but not cold (about an hour).
In the bowl of a stand mixer, cream together sugars, browned butter, and milk.
Beat in one egg until combined.
Mix in the flour, salt, espresso powder, and baking soda until smooth.
Fold in the chocolate chips.
Cover the dough and refrigerate for at least 24 hours.
Preheat the oven to 375°F.
Scoop 2 Tbsp-sized balls out onto a Silpat or parchment-lined baking sheet. Do not roll them smooth, but allow the balls to have some lumps.
Bake for 10-12 minutes. Cool for 5 minutes on the sheet, and then remove them to a cooling rack.