Preheat oven to 350°F and grease or line a mini muffin tin.
Whisk melted butter, sugar, eggs, and vanilla; mix in cocoa, flour, and salt.
Fill muffin cups ⅔ full and bake 10 to 12 minutes.
Cool brownies 5 minutes in pan, then transfer to a rack to cool completely.
Beat butter, sugars, milk, and vanilla; mix in flour, salt, and mini chocolate chips.
Add a small scoop of cookie dough onto each brownie bite.
Chill about 30 minutes, then serve.