Line a shallow 8 X 8 baking dish with parchment paper and set aside.
Preheat your oven to 325”F. While your oven is heating up, make the lemon curd.
To make the lemon curd, prepare a double boiler with 2 inches of water in the bottom pan. Bring to a gentle simmer.
Add the egg yolks, sugar, lemon zest and lemon juice to the top pan. Whisk together over the steam until combined well. Keep whisking for a few minutes until the curd has thickened and coats the back of a spoon. About 10 to 15 minutes or so. Turn off the flame and whisk in the butter until melted. Transfer the curd to a bowl and cover with plastic wrap. Refrigerate until cooled completely
In the bowl of a food processor add the flour, butter, lemon zest and sugars. Pulse together until a dough forms. Use a spatula and transfer the dough to the prepared baking dish. Press it on top and to fill in the corners.Bake the shortbread in the preheated oven until golden, about 35 to 40 minutes or so. Take the shortbread out of the oven and top with the lemon curd. Transfer to the refrigerator until chilled.
Use a sharp knife to cut the lemon bars into 2x2 inch squares and sprinkle with powdered sugar on top.