Preheat the oven to 350°F.

Spray a 9x13-inch baking pan with nonstick cooking spray, and set aside.

To make the crust, place the softened butter, sugar, vanilla, and salt in a medium bowl and use a hand mixer to combine. Add the flour and continue mixing until a soft dough forms.

Transfer the dough to the baking pan. Using a tamper, clean hands, or the bottom of a heavy glass, press the dough into an even layer.

Bake the crust on middle rack of oven until slightly golden at the edges, 15-18 minutes. While the crust bakes, prepare the filling.

Place the eggs, sugar, lemon zest, and lemon juice into a large mixing bowl. Mix with a hand mixer until the mixture is just smooth and combined. Sift the flour into the bowl. Mix until the flour is fully incorporated. Scrape down sides of bowl with a rubber spatula as needed.

Carefully remove the baking pan from the oven. Pour the lemon filling over the crust. Tap pan on the counter to reduce air bubbles in the filling.

Return pan to oven and continue baking until the filling sets and a toothpick inserted in the center comes out clean, 30-35 minutes.

Check to see that bars are done. Remove from oven or add time as needed.

Allow the bars to cool for 20 minutes at room temperature, then transfer to the refrigerator. Chill for at least 2 hours before slicing and serving.

Just before serving, sift a generous layer of powdered sugar over the bars. Slice and serve.