1/2cupunsalted butter, at room temperature, cut into 8 pieces
1/8tspfine salt, omit if using salted butter
Lemon Filling:
1 1/2cupswhite granulated sugar
1/3cup + 1 Tablespoonall purpose flour
3largeeggs, at room temperature
1/4cupfresh lemon juice
For topping after baking:
Additional confectioners' sugar
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Instructions
Take your eggs and butter out of the fridge ahead of time, so they both come to room temperature before starting the recipe.
Preheat oven to 350F (not fan-assisted), with rack in centre of the oven.
Prepare an 8-inch square metal baking pan with parchment paper, covering bottom and sides and overhanging the sides to use as handles to remove from the pan later. Set aside. *For glass pans, reduce oven temperature by 25F.
Prepare the Shortbread Base: Whisk together the flour, confectioners' sugar and salt. Add the cubed butter and cut into the flour mixture with a pastry cutter or just use your fingertips to rub it in to the flour. Pour into prepared baking pan and press firmly and evenly into the bottom. Bake in preheated oven for 15-18 minutes, or until set and just starting to colour. Remove from oven and let cool while you mix up the filling. (Leave oven on at 350F).
Make the Lemon Filling: combine all the filling ingredients in a medium bowl and whisk together well until smooth. *Don't "whisk" too vigorously, but rather use the whisk like a spoon and stir the mixture. You don't want to whisk too much air into the batter.
Pour filling over the baked crust and return to the oven. Bake until the filling is completely set and it doesn't jiggle at all when lightly tugging the pan, about 20-25 minutes. *Important that you test by jiggling the pan. If there is any jiggle at all, leave in the oven a few more minutes until there is no jiggle. In my oven, that is usually 23-25 minutes.
Remove from oven and let cool completely in the pan. *I like to refrigerate for an hour or so for easiest slicing, but it is not necessary. Just be sure they are completely cool. Lift squares out of pan by lifting with the edges of the parchment paper. Use a large, sharp knife to slice into 9 squares. Sift top with confectioner's sugar just before serving. Store in the refrigerator or they also freeze well.
Notes
Be sure to read the notes above the Recipe Card for more tips on making this recipe. You'll also find Step-by-Step photos of the process of making these squares.