Prep Your Battlestation. Preheat your oven to 350°F (175°C) and line your 9x13 inch baking pan with parchment paper, leaving some overhang for easy removal later. (Future you will thank present you for this step.)
Crust Construction. In a medium bowl, whisk together the flour, sugar, and salt for the crust. Add the cold cubed butter and vanilla extract, then use your fingers (or a pastry cutter if you're fancy) to work the butter into the dry ingredients until the mixture resembles coarse crumbs. Think wet sand texture – the kind that's perfect for sandcastles, not the kind that gets in your swimsuit.
Press and Bake. Dump this mixture into your prepared pan and press it firmly and evenly into the bottom. Don't rush this part – an even crust is a happy crust. Bake for 15-20 minutes until the edges are just barely turning golden. Remove from the oven but keep it running – we're not done yet!
Lemon Filling Extravaganza. While the crust is baking, make your filling. In a large bowl, whisk together the eggs and sugar until well combined. Add the lemon zest, lemon juice, and flour, then whisk until smooth. If you see some tiny flour lumps, don't panic – they'll bake out. Pour this mixture over the hot crust as soon as it comes out of the oven.
The Final Bake. Return the pan to the oven and bake for another 20-25 minutes, until the filling is set and doesn't jiggle in the center when you gently shake the pan. You're looking for a slight wobble like a firm Jell-O, not a wave pool.
The Cooling Game. This is the hardest part – patience. Let the bars cool completely in the pan at room temperature, then refrigerate for at least 2 hours (overnight is even better). I know, I know – the waiting is torture, but cutting into warm lemon bars is like trying to slice pudding. Trust me.
The Grand Finale. Once cooled and chilled, use the parchment overhang to lift the entire slab out of the pan. Cut into 16 squares with a clean, sharp knife, wiping the blade between cuts for Instagram-worthy precision. Just before serving, dust generously with powdered sugar for that classic finishing touch.