Cream butter with a mixer and add dry cake mix and egg. Mix until it comes together in a stiff cookie batter. Reserve 1/3 of batter for topping

Line a large square baking dish, like a 10 x 10, with parchment paper. {“9 x 13” will yield a thinner bar} Spray the paper to prevent it from sticking to the baked cookies.

Pat 2/3 of dough onto sprayed paper in dish forming an even layer. Top with chocolate chips and desired amount of coconut. Pour milk over all. Drop remaining batter in small pieces over top and gently press down.

Bake at 350 for 25-35 minutes, until mixture is set and golden. Place dish on wire rack to cool. Let cool for 3-4 hours. Remove from pan by lifting out paper. Top with lemon zest. Cut into squares or bars. Place cookies in individual cupcake papers for ease of serving. Can be kept covered at room temperature or in refrigerator.