Line an 8- or 9-inch square pan with parchment, leaving overhang for lifting.
Stir graham crumbs, sugar, and salt in a bowl. Pour in melted butter and mix until evenly moistened.
Press the crumb mixture firmly into the pan to form an even crust. Chill while you make the filling.
Beat softened cream cheese and powdered sugar until completely smooth and fluffy.
Blend in lemon zest, lemon juice, vanilla, and sour cream until creamy with no streaks.
Whip the heavy cream to medium peaks. Gently fold it into the lemon filling until airy.
Spread the filling over the chilled crust and smooth the top. Cover and refrigerate at least 4 hours, until set.
Swirl or spread lemon curd over the set cheesecake. Garnish with extra zest, slice into bars, and serve cold.