Preheat oven to 350°F. Line a 9x13 inch baking pan with parchment paper, letting excess hang over the sides for easy removal. Tap the pan gently to ensure parchment sits flat.

In a medium bowl, whisk together 2 cups flour, 0.5 cup granulated sugar, and 0.25 teaspoon salt until evenly combined. This should take about 1 minute and look like fine sand with no lumps.

Add 1 cup softened butter (cut into small cubes, about the size of peas) to the flour mixture. Using your fingertips, rub the butter and flour together until the mixture resembles coarse breadcrumbs with pea-sized pieces of butter still visible. This takes 3-4 minutes.

Transfer the mixture to the prepared pan and press it firmly and evenly into the bottom using the bottom of a measuring cup or your hands. The crust should be compact but not overly dense, and should reach all corners. This takes about 2 minutes.

Bake the crust for 12-15 minutes at 350°F. The crust is ready when it's light golden brown around the edges and the surface looks dry and matte. Do not over-bake—it should still be pale in the center. Checkpoint: The crust should look set but still slightly soft.

While the crust bakes, crack 4 large eggs into a medium bowl. Add 1.5 cups granulated sugar. Whisk vigorously for 2-3 minutes until the mixture is pale yellow, thick, and falls in ribbons from the whisk. This is important for a light, fluffy filling.

Add 0.5 cup fresh lemon juice (about 3-4 lemons, squeezed and strained to remove pulp) to the egg mixture. Stir gently but thoroughly for about 1 minute until completely combined. The mixture should be smooth and uniform in color.

Stir in 2 tablespoons lemon zest, folding it in gently with a rubber spatula. Use a microplane or fine grater for the zest so no large pieces remain. This takes about 1 minute.

In a small bowl, whisk together 3 tablespoons flour and 0.5 teaspoon baking powder for about 30 seconds, breaking up any lumps. This prevents the filling from being too dense.

Add the dry flour mixture to the lemon mixture. Using a rubber spatula, fold gently until just combined—fold about 8-10 times until no dry streaks remain. Do not over-mix, as this can make the filling dense. This takes about 1 minute.

Remove the hot crust from the oven. Immediately pour the lemon filling over the hot crust, spreading it evenly to the edges with a spatula. The filling should reach all corners and be about 0.5 inch thick. Do this quickly so the filling sets evenly. Checkpoint: The filling should be smooth and level across the pan.

Bake the bars for 18-22 minutes at 350°F. The filling is done when the edges are set and pale golden, but the very center (about a 2-inch square) still jiggles slightly when you gently shake the pan. The surface should look matte and dry, not wet or glossy. Do not over-bake, or the filling will be rubbery.

Remove the pan from the oven and place it on a wire cooling rack. Let the bars cool to room temperature—this takes about 1 hour. The filling will continue to set as it cools.

Once cooled, transfer the pan to the refrigerator and chill for at least 2 hours. Cold bars are easier to cut cleanly. You can chill overnight for best results.

Using the parchment paper overhang, lift the entire bar out of the pan onto a cutting board. Using a sharp knife dipped in hot water and wiped dry between cuts, slice into 16-20 squares. The knife should glide through cleanly, leaving sharp edges.

Place each bar on a serving plate or platter. Dust generously with 2 tablespoons powdered sugar just before serving, using a fine-mesh sieve for even coverage. The sugar will cling to any moisture on the surface, creating a beautiful finish.

Serve at room temperature or chilled. Lemon bars are best enjoyed within 1-2 hours of dusting for optimal texture, though they stay fresh for up to 4 days when stored in an airtight container.