Preheat the oven to 350 degrees Fahrenheit and line an 8x8-inch baking pan with parchment paper.

Pulse the flour, sugar, and salt in a food processor or whisk in a medium bowl.

Add the butter and pulse or cut it into the flour with a pastry cutter until a sandy texture forms.

Pour it into the prepared pan and smooth it out using the back of a spoon. (It will be very crumbly so don’t worry if it isn’t compressed, the butter will melt in the oven and the dough will form a nice hard crust while baking.)

Bake for 10-15 minutes, or until lightly golden.

While the crust bakes, whisk together the sugar, lemon juice, eggs, flour, lemon zest, vanilla, and a pinch of salt until smooth.

Pour the filling over the warm crust and return to the oven for 20-25 minutes, or until the top is dried out and the edges are golden, but the center is still jiggly.

Let the bars cool completely in the pan, then dust generously with powdered sugar before slicing and serving.

Optional: refrigerate for an hour to let the custard set well if yours is too soft to slice right out of the oven.