Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out later.
In a large bowl, beat the softened butter and sugar until light and fluffy, about 2-3 minutes. Add flour and salt, mixing until just combined.
Gently press the dough evenly into your prepared pan, creating a smooth surface that extends to all corners.
Bake the crust for 15-20 minutes until just beginning to turn golden at the edges.
While the crust bakes, whisk together sugar and flour in a medium bowl. Add eggs one at a time, whisking well after each addition until the mixture is smooth.
Stir in lemon juice and zest, mixing until everything is fully incorporated.
Pour the lemon filling over the hot pre-baked crust immediately after removing it from the oven.
Return the pan to the oven and bake for 20-25 minutes more, until the filling is set but still has a slight jiggle in the center.
Allow the lemon bars to cool completely at room temperature (about 1 hour) before transferring to the refrigerator to chill for at least another hour.
Once chilled, use the parchment paper overhang to lift the entire slab out of the pan. Dust generously with powdered sugar using a fine-mesh sieve, then cut into squares with a clean knife.