Warm up your oven to 350°F. Give an 8x8-inch baking dish a generous buttering, then cozy it up with parchment paper, making sure it hangs over on at least two sides for an easy lift once your delicious bars are baked.

Create the shortbread crust: Grab a large bowl and whisk together the flour, powdered sugar, and salt. Pour in the melted butter and vanilla, then stir with a spatula until you have a smooth, greasy dough. Pop the dough into your prepared pan and gently press it down with your hands, making sure it covers the bottom and creeps up the sides by about ⅛ inch.

Let your crust bake for about 18 to 20 minutes until it turns a lovely light brown around the edges. Once it’s out of the oven, give it a playful poke with a fork.

Meanwhile, prepare the lemon filling: Put the sugar in a large bowl. If you’re adding lemon zest, mix it into the sugar using your fingers to release the fragrant oils and enhance the flavor.

Stir in the flour and whisk until mixed, then blend in the eggs and finally the lemon juice.

Pour the mixture over the hot crust and bake for 20 to 25 minutes, until the filling is fully set. A gentle shake of the pan should reveal no jiggle in the filling.

Take out of the oven and allow to cool for an hour at room temperature. Then, move to the refrigerator and let it chill for an additional two hours.

Sprinkle powdered sugar over the chilled bars, cut them into slices, and serve.