My husband loves anything with lemon in it - especially these lemon bars. They do require more effort than the average lemon square recipe, but the effort is well worth the look of bliss on my husband's face!
Preheat the oven to 350 degrees. Line a 9-inch square pan with foil, then coat lightly with "Pam". If you are going to serve the squares directly from the pan, there is no need to line with foil.
Process the flour, powdered sugar, and salt in a food processor until combined, about 3 seconds. Sprinkle the 8 tablespoons of butter over the top and pulse until the mixture is pale yellow and resembles coarse crumbs, about 8 pulses.
Sprinkle the mixture in the prepared pan and press firmly into an even layer, using your fingers. Bake until the crust starts to brown, about 20 minutes.
While the crust is baking, whisk the yolks, and whole eggs together in a medium nonreactive saucepan. Whisk in the sugar until combined, then whisk in the lemon juice, lemon zest, and a pinch of salt. Add the 4 tablespoons of butter and cook over medium-low heat, stirring constantly, until the mixture thickens slightly and registers 170 degrees on an instant read thermometer, about 5 minutes.
Strain the mixture immediately into a nonreactive bowl and stir in the cream. Pour the warm lemon curd over the hot crust (it is important that both the lemon curd and crust are hot - this ensures that the filling cooks through evenly). Bake until the filling is shiny and opaque and the center jiggles slightly when shaken, 10 to 15 minutes.
Let cool completely on a wire rack, about 2 hours, before removing the squares from the pan using the foil and cutting into 9 squares (smaller if you like). Dust with powdered sugar before serving.