Preheat oven to 350°F (175°C) and line an 8×8-inch pan with parchment paper for easy lifting.
Mix flour, powdered sugar, and salt, then cut in cold butter until crumbly.
Press into the pan and bake 15–18 minutes until lightly golden; let cool slightly.
Whisk egg yolks and condensed milk, then add lemon juice, zest, vanilla, and salt until smooth. Pour over the warm crust and spread evenly.
Bake 15–20 minutes until edges are set and center slightly wobbly.
Cool 30 minutes, then chill 1–2 hours or overnight. Lift out, dust with powdered sugar, slice, and top with whipped cream or lemon slices.