1. Preheat the oven to 350 degrees. Line an ungreased 8×8-inch glass baking dish with crossing strips of parchment, which will make it easier for you to lift the lemon bars out of the dish after baking.
2. In a mixing bowl or the bowl of a stand mixer with paddle attachment, combine flour, sugar, salt, and lemon zest; mix gently until combined. Add butter and mix until the dough is crumbly (it will not come all the way together yet). Next, use your hands to knead the dough until it comes together in a ball. This will take some time, so be patient. The dough will come together as the warmth of your hands lightly melts the butter.
3. Press the dough into the prepared baking dish over the parchment strips. Again, be patient as you work the dough into an even layer. Make the layer as even as possible, without any rise at the edges, patting it down with your fingers. Bake for 5 minutes and then remove to cool slightly while you prepare the filling. This short baking time just helps to start setting the crust, but it will not be fully baked yet.
4. Meanwhile, make the filling. In a separate bowl, combine the eggs, granulated sugar, cornstarch, and lemon juice (not the lemon zest yet). Mix until the sugar and cornstarch are dissolved. Strain the mixture through a sieve (this step is not necessary, but makes for a very smooth and nice-looking filling). Stir the lemon zest in and gently pour the filling over the par-baked crust. Return to the oven and bake for 30 minutes without opening the oven.
5. Remove baking dish from oven and let bars cool 15 minutes in the pan. Run a knife around the outer edge of the parchment, and very gently lift up on the parchment flaps to remove the full slab to a cutting board. If you prefer perfect squares, use a Chef’s knife to cut off the outer 1/8-inch edge on all four sides, then cut into 16 squares. Refrigerate bars at least 1 hour before serving, then top with desired garnishes.  Store any leftovers in the refrigerator for up to 1 week.

How to Make Lemon-Infused Whipped Cream: 8 to 24 hours before serving, add 1 tablespoon lemon zest to the heavy cream (you can add the zest right to the heavy cream container; close and store in the refrigerator). Before serving, in a stand mixer or hand-held mixer with whisk attachment, combine the lemon-flavored heavy cream and powdered sugar. Whip until soft peaks form. Serve immediately or store in the coldest part of the refrigerator for up to 4 hours before serving; may need to re-whip before serving.