• Start by zesting and juicing the lemons until you have a tablespoon of zest and 1 cup of lemon juice.
• Preheat oven to 350°F / 180°C. Prepare a glass or ceramic coated 13x9 baking dish by spraying the bottom and sides with cooking spray or greasing with butter. Trim some parchment paper to make a sling and spray or butter the top of that as well. Set it aside.

Shortbread Crust:

• Now make the shortbread crust. In a mixing bowl, add 1 ¾ cups all-purpose flour, ⅔ cup granulated sugar, ¼ cup corn starch, and ½ teaspoon salt. Whisk to combine everything. Pour in the melted ¾ cups unsalted butter (and 1 teaspoon of extract if using any) and mix with a wooden spoon or fork until a loose dough forms.
• Dump the dough into the prepared 13x9 baking dish and spread it out across the bottom. Using your hands, press the dough down into the dish and try to spread and level it out as evenly as possible. Bake the shortbread layer for 18-22 minutes, until it just starts to show some browning.

Limoncello Curd:

• While the crust is baking, prepare the custard layer. In another mixing bowl, add 2 14-oz cans of sweetened condensed milk, 2 eggs, and 4 egg yolks. Whisk together until no visible streaks of egg remain.
• Now add 1cup of lemon juice, 1 tablespoon lemon zest, and 3 tablespoons of limoncello. Whisk again until the lemon juice is fully combined and there’s no layer of separated juice.
• As soon as the bottom crust has cooked, remove the dish from the oven. Pour the lemon mixture over the hot crust and make sure the layer is fully spread out and even. Place the baking dish back in the oven and lower the temperature to 325°F / 162°C. Bake for another 20 minutes. The creamy limoncello lemon bars are done when the top layer no longer looks wet and barely jiggles at all when you shake the dish.
• Allow the limoncello bars to cool at room temperature for at least 1-2 hours, and then I prefer to also refrigerate another 1-2 hours until cool and firm. Once fully cooled to your preference, remove the creamy limoncello lemon bars from the baking dish by lifting straight up with the parchment sling.
• For the cleanest looking lemon bars, run a sharp knife under hot water and wipe clean between each slice you make. Optionally dust the tops with powdered sugar and serve.