Preheat oven to 350°F. Place one rack in the middle of the oven.

In a medium bowl, combine melted butter, ½ cup powdered sugar and 2 cups flour. Stir until all ingredients are incorporated (should resemble wet sand). Press mixture into a 9 x 13 baking dish in an even layer. Bake for 15 minutes.

Meanwhile, lightly whisk together eggs, lemon juice and lemon zest in a medium bowl. Add ¼ cup flour and 2 cups granulated sugar, whisking to combine. After 15 minutes, remove the baked crust from the oven. Immediately pour the egg-lemon mixture on to the hot crust. Return the baking dish to the oven for an additional 25 minutes. Let cool slightly before serving.

Finish by cutting into bars and top with a dusting of powdered sugar.