Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving some overhang for easy removal. Lightly grease the parchment paper with butter or cooking spray. Pro tip: The parchment paper overhang acts like handles, making it super easy to lift the bars out of the pan once they're cool.

In a large mixing bowl, whisk together the flour, powdered sugar, and salt. Add the cold, cubed butter and use your fingers or a pastry cutter to work it into the flour mixture until it resembles coarse crumbs with some pea-sized butter pieces. Pro tip: Cold butter is key here – it creates those lovely flaky layers in your crust.

Press the mixture firmly and evenly into the bottom of your prepared pan. Use the bottom of a measuring cup to help create an even surface. Pro tip: Really press down firmly – this prevents the crust from being too crumbly and helps it hold together perfectly.

Bake the crust for 18-20 minutes, until the edges are lightly golden. Remove from the oven but keep the oven on – you'll need it for the second bake. Pro tip: Don't overbake the crust at this stage since it will continue cooking with the lemon topping.

While the crust bakes, whisk together the eggs and granulated sugar in a large bowl until well combined. Add the flour, lemon juice, lemon zest, and salt, whisking until the mixture is smooth and no flour lumps remain. Pro tip: Strain the lemon juice if you want an ultra-smooth topping without any pulp.

Pour the lemon mixture over the warm crust, spreading it evenly to the edges. Pro tip: Pouring over the warm crust helps the layers bond together beautifully.

Return the pan to the oven and bake for 20-25 minutes, until the lemon topping is set and no longer jiggly in the center. The top should look matte rather than shiny when done. Pro tip: The center should be completely set but not browned – overbaking can make the topping rubbery.

Allow the bars to cool completely in the pan, about 2 hours. For the cleanest cuts, refrigerate for at least 1 hour before cutting. Pro tip: Wipe your knife clean between cuts for the prettiest, most professional-looking bars.

Lift the bars out using the parchment paper overhang, then cut into squares. Dust with powdered sugar just before serving. Pro tip: Cut into 24 squares for standard serving sizes, or make them smaller for parties and larger gatherings.