This is a lemon bar unlike any other--it comes with a tropical twist. Most lemon bar recipes yield a high filling-to-crust ratio, but this one changes it up a bit, with about equal amounts of crunchy, buttery crust and surprisingly tart filling. The crust includes a generous handful of toasted coconut to enliven its already deliciously crispy texture, and we bake it to a deep golden brown so it retains a satisfying crunch when topped with the filling.