Preheat the oven and line your baking pan with parchment paper. I mix flour, powdered sugar, and melted butter until crumbly but cohesive. Press it evenly into the pan and bake until lightly golden. This creates a sturdy base for the filling.
In a separate bowl, I whisk eggs with sugar until pale and smooth. Fresh lemon juice, zest, baking powder, vanilla, and salt are added next. This mixture should look silky and smell bright before pouring it over the crust.
Sprinkle shredded coconut evenly across the lemon layer. I gently press it down so it sticks slightly. This step ensures the coconut bakes into the filling rather than floating on top.
Bake until the center no longer jiggles and the coconut turns lightly golden. The bars will continue to firm as they cool. Avoid overbaking, or the lemon layer can become rubbery.
Let the bars cool completely in the pan. I chill them briefly before slicing for cleaner edges. Use a sharp knife and wipe it between cuts for bakery-style bars.