Make brownie batter according to directions on box. (You can make both boxes together in a large bowl, just make sure you add the ingredients for both boxes.)
Pour half of brownie batter into a greased 9x13-inch pan.
In a medium bowl, stir together coconut, sweetened condensed milk, vanilla extract, and mini chocolate chips. Spoon evenly over brownie batter.
Pour remaining brownie batter over coconut mixture.
Bake at 350 degrees for about 45 minutes. Let cool before cutting into squares.