Spread flour out onto a rimmed 18 x 13-inch baking sheet. Bake in preheated oven 7 minutes, or until flour temperature registers 160 degrees on an instant-read thermometer.
Transfer flour to a cool dish and place in the fridge to cool completely.
While flour cools, combine the softened butter, brown sugar, and sugar in a bowl and use a hand mixer to beat until light and fluffy. Mix in the milk and vanilla, scraping the sides of the bowl as needed.
Add in the flour, cocoa, and mix until combined. Fold in the chocolate chips. If the dough seems too thick to your liking, add milk 1 tsp. at a time.
You can enjoy the dough right away, or chill in an airtight container in the fridge for up to 1 week or in the freezer up to 1 month.