Shortbread Crust
1-Lightly spray an 8-inch square baking pan: Lightly spray an 8-inch square baking pan with a flour-based baking spray. Set to the side. If you’d like, spray the pan, then place a parchment paper sling in it to make cutting the lemon bars easier later. To prevent the parchment paper sides from collapsing into the bars during baking, you can place a binder clip on top of the paper.
2-Using a hand mixer or a stand: Using a hand mixer or a stand mixer fitted with a paddle attachment, beat together the unsalted butter, all-purpose flour, and powdered sugar until the shortbread bottom layer forms. It will resemble light yellow loose crumbs. Pat the shortbread layer into the bottom of the prepared 8-inch square baking pan. Then place in the freezer or refrigerator for about 10-15 minutes to chill. Skip the chilling if you’re using a glass baking dish.
3-While the shortbread layer chills, adjust the: While the shortbread layer chills, adjust the oven rack to the 2nd level position (just above center) and preheat the oven to 350ºF.
4-Place the pan in the oven and: Place the pan in the oven and bake for 15-18 minutes at 350ºF or until it’s light golden brown.
5-Remove from the oven and allow to: Remove from the oven and allow to cool slightly while you prepare the lemon curd filling. You can leave the oven on, or turn it off while you make the lemon curd filling. If you turn it off, remember to preheat it again to 350ºF.

Lemon Curd Filling
6-Grate a lemon with a fine grater,: Grate a lemon with a fine grater, adding the zest to a small bowl. Then cut each lemon in half and with a lemon juicer, squeeze out the lemon juice from each lemon. Sift the all-purpose flour into a small bowl.
7-Using a hand mixer or a stand: Using a hand mixer or a stand mixer fitted with a whisk attachment, mix together the lemon juice, lemon zest, eggs, granulated sugar, and all-purpose flour on medium-high speed until well blended.
8-Pour the lemon curd filling into the: Pour the lemon curd filling into the slightly cooled crust, then bake for 25-30 minutes at 350ºF, or until the top is almost set and the center jiggles slightly. I recommend checking them at the earliest recommended baking time. Leaving them in too long can cause a thin crust to form over the top. The lemon bars are still good, though, if this happens!
9-Remove from the oven and allow lemon: Remove from the oven and allow lemon bars to cool completely. Then cover and place into the refrigerator to chill and set for a minimum of 1 hour (overnight is my preference). When ready to serve, dust with powdered sugar and cut using a well-sharpened knife.
10-Keep lemon bars stored in an airtight: Keep lemon bars stored in an airtight container in the refrigerator for up to 5 days.