1. Preheat oven to 275ºF. Butter and flour a 9×13 baking dish and set aside.
2. In a bowl mix the butter, flour and brown sugar. Using clean hands, pinch it together until a dough forms. Press the dough into the bottom of the 9×13 baking dish and bake for 12-15 minutes, or until the edges are lightly browned.
3. While the crust is baking, make the filling. In a large mixing bowl combine the lightly beaten eggs, brown sugar, coconut, flour, baking powder, salt and vanilla. Using a wooden spoon, combine all of the ingredients until everything is completely incorporated.
4. When crust has finished baking, remove it from the oven and all it to cool for 10 minutes. Increase the oven temperature to 350ºF.
5. Once the oven has hit 350º spread the mixture on top of the crust and spread it smooth with a wooden spoon. Bake it for 22-25 minutes, or until the coconut is golden brown and the top is set.
6. While the coconut is baking, make the glaze. In a small mixing bowl whisk together the melted butter, confectioners sugar and lemon juice so that is completely smooth.
7. When the squares have finished baking remove them from the oven and drizzle them evenly with the glaze. The glaze will sink into the squares – that is alright.
8. Allow squares to cool for 1 hour on a wire rack. Then cover them with plastic wrap and refrigerate for 2 hours until they are set. Cut into 2″ squares and serve.