Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper.

Combine all-purpose flour, granulated sugar, and salt in a mixing bowl. Cut in cold unsalted butter until it resembles coarse crumbs. Stir in vanilla extract.

Press two-thirds of the crumb mixture into the bottom of the prepared pan to form the crust.

Bake the crust in the preheated oven for approximately 15 minutes, or until lightly golden.

Whisk together eggs and granulated sugar until smooth. Mix in flour, lemon juice, lemon zest, and salt until well combined.

Pour the lemon filling over the baked crust, and sprinkle the remaining crumb mixture on top.

Bake for 20 to 23 minutes, or until the filling is set and the topping is golden brown.

Cool for at least 30 minutes at room temperature, then chill in the refrigerator for at least 1 hour before slicing.

Lift the bars out of the pan using the parchment overhang, slice, and serve.