Evenly spread the flour on a baking sheet. Bake for 5 minutes to kill any harmful bacteria. Let cool to room temperature.
Add the butter to a large skillet over medium-high heat. Cook, stirring occasionally, until the butter turns dark brown and smells nutty, about 5 minutes. Watch carefully so the butter does not burn.
Remove the pan from the heat and pour the brown butter into a heatproof liquid measuring cup. Let cool for a minute or 2, then give it a stir and carefully pour in enough water to bring it back up to 1½ cups of liquid. Let cool to room temperature.
In a large bowl, combine the cooled browned butter, granulated sugar, and brown sugar. Mix with an electric hand mixer or whisk until evenly combined.
Add the espresso powder, salt, vanilla, milk, and cooled flour and mix until combined.
Fold in the chocolate chips and chopped chocolate until incorporated.
Refrigerate the dough for 30 minutes, until firm. The cookie dough will keep in the refrigerator for up to 5 days.
Need easy dinner ideas?
These meals will make your weeknights way simpler. (And tastier!)