original recipe on allrecipes.com, but modified it. And by modified, I mean I love the filling and use regular brownie mix. Especially when said mix is on sale for $1 at King Soopers.
1 box brownie mix (family size for a 9x13 inch pan)
4 cups flaked coconut
1 can fat-free sweetened condensed milk
1 T vanilla
Prepare the brownie mix following instructions. I use a 9x9 inch silicone pan so they are deep dish brownies. Pour half the brownie batter in the pan. Mix the coconut, milk and vanilla in a bowl. Drop / smooth onto the layer of brownie batter. Top with remaining batter. If you want to, you can add chocolate chips to the brownie batter, just for fun. Bake according to the instructions for a 9x9 pan, probably 35-40 minutes.