1. Prepare the Crust:

1. Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
2. In a large bowl, combine 2 cups of flour, 1/2 cup granulated sugar, and 1/4 teaspoon salt for the crust and crumb topping. Add the cold cubed butter and use a pastry cutter or your hands to mix until the mixture resembles coarse crumbs.
3. Press half of the crumb mixture firmly into the prepared pan to form the crust. Set the remaining aside for the topping.
4. Bake the crust in the preheated oven for about 15 minutes, or until it starts to turn golden. Remove from the oven and set aside to cool slightly.
5. In another bowl, whisk together 1 cup granulated sugar, 2 tablespoons flour, and 1/4 teaspoon baking powder for the filling. Add the eggs one at a time, whisking to combine after each addition.
6. Stir in the lemon juice, lemon zest, and salt until fully incorporated.
7. Pour the lemon filling over the slightly cooled crust, spreading it evenly with a spatula.
8. Sprinkle the reserved crumb topping evenly over the lemon filling.
9. Return the pan to the oven and bake for an additional 25-30 minutes, or until the top is lightly golden and the filling is set.
10. Allow the bars to cool completely in the pan on a wire rack. Once cooled, use the parchment overhang to lift the bars out of the pan and onto a cutting board.
11. Dust with powdered sugar, if desired, before cutting into squares.