Prepare the brownie batter according to the package instructions. Bake and let cool completely.
Cream together softened butter, brown sugar, and granulated sugar until fluffy. Add milk and vanilla, then mix in flour and fold in mini chocolate chips.
Scoop 1 tablespoon of dough, roll into balls, and place on a parchment-lined tray. Chill if dough is too soft.
Cut cooled brownies into squares. Flatten each square, place a cookie dough ball in the center, and wrap the brownie around it to seal.
Melt chocolate candy melts and dip each brownie bomb into the melted chocolate, letting excess drip off. Place on parchment-lined baking sheet.
Sprinkle with optional toppings before the chocolate sets. Refrigerate for 30 minutes to firm up the chocolate.