How to Make It
Heat oven to 350° F. Line an 8-inch square baking pan with 2 crisscrossed pieces of parchment, leaving an overhang on all sides.
Pulse the graham crackers, 2 tablespoons of the sugar, and 1/2 teaspoon of the salt until fine crumbs form in a food processor. Add the 6 tablespoons of melted butter and pulse to combine. Using a straight-sided dry measuring cup, press the mixture into the prepared pan. Bake until firm, 8 to 10 minutes. Let cool.
Meanwhile, whisk together the eggs, egg yolks, and the remaining cup sugar in a bowl; set aside. Combine the orange zest and juice, lemon zest and juice, cream, the remaining 4 tablespoons of butter, and the remaining 1/2 teaspoon salt in a medium pot. Cook over medium heat, stirring occasionally, until the butter is melted, 2 to 3 minutes.
Slowly add 1/2 cup of the juice mixture to the egg mixture, whisking constantly, until combined. Return to the pot with the remaining juice mixture and cook, stirring constantly, until the mixture thickens to a custard and coats the back of a spoon, 12 to 14 minutes.
Pour the mixture through a fine-mesh sieve over the cooked crust. Smooth the surface with an offset spatula or spoon. Refrigerate until firm, at least 12 hours and up to 3 days.
Holding the paper overhang, lift the bars out of the pan and transfer to a cutting board. Cut into 16 squares.
Tip: The longer these bar are chilled, the stiffer and easier to cut they will be.