Preheat the oven and line a square baking pan with parchment paper allowing for an overhang on the sides.

Cream the room temperature butter with sugar and vanilla in a mixer until the texture is light and fluffy.

Incorporate the flour and salt on low speed until the mixture resembles small crumbles.

Press the dough firmly into the bottom of the prepared pan and dock the surface with a fork.

Bake the crust until the edges reach a beautiful golden brown color then remove from the heat.

Rub fresh lemon zest into the granulated sugar in a saucepan to release the fragrant citrus oils.

Whisk in the flour and cream of tartar followed by the whole eggs and egg yolks until the mixture is smooth.

Stir in the fresh lemon juice and cook over medium-low heat while stirring constantly until the filling thickens.

Pass the thickened lemon curd through a fine-mesh strainer to ensure a silky texture.

Pour the strained filling over the warm crust and bake again until the center is set.

Allow the bars to cool completely at room temperature before transferring them to the refrigerator to chill.

Lift the bars out using the parchment paper, dust generously with powdered sugar, and slice with a clean knife.