Heat oven to 350°F. Line an 8-inch square pan with parchment, leaving overhang.
Whisk flour, powdered sugar, salt, and 1 tsp lemon zest in a bowl.
Stir in melted butter until the mixture looks like damp sand.
Press crust firmly into the pan. Bake 15 minutes, until set and lightly golden.
Beat cream cheese until smooth. Blend in condensed milk and sour cream until creamy.
Whisk in beaten eggs, remaining lemon zest, lemon juice, vanilla, and salt just to combine.
Pour filling over warm crust and smooth the top.
Bake 18–20 minutes, until edges are set and the center still jiggles slightly.
Cool in pan on a rack for 1 hour. Chill at least 2 hours until firm.
Dust with powdered sugar. Lift out by parchment, slice into bars, and serve.