1. In a medium-sized saucepan over medium heat, stir together the lemon juice, sugar, and cornstarch.
2. Meanwhile, in a mixing bowl, whisk together the eggs and egg yolk.
3. When the sugar has completely dissolved, temper the eggs by drizzling in about a half a cup of the hot mixture into the egg yolks while whisking constantly.  Then pour the contents of the mixing bowl into the saucepan.
4. Stir frequently until the mixture begins to thicken - this will take several minutes.  Remove from heat.

Make and Bake The Crust

1. Preheat oven to 350F.  In a clean mixing bowl, stir together the graham cracker crumbs, sugar, and lemon zest.  Add the melted butter and stir well until all of the crumbs have evenly absorbed the butter.
2. Lightly spray a 9x13 glass baking dish with cooking spray.  Add the graham cracker crumb mixture and press into the pan in an even layer.  Use the bottom of a measuring cup or other flat surface to firmly pack the crust into the pan.
3. Bake on center rack for 8-10 minutes - you want the crust to darken noticeably and you should be able to smell the graham crackers.  Remove from oven.

Bake The Bars

1. Pour the lemon curd over the hot crust and spread out evenly.  Bake for an additional 12-15 minutes until the curd isn't super jiggly in the middle (it will still look a little loose and sticky). 
2. Allow to cool on counter for about 20 minutes, and then chill in the refrigerator for several hours before attempting to cut into squares.  Dust with powdered sugar if desired, and store leftovers in the refrigerator.