Preheat oven to 350. Line a 7x11 Pyrex or 8x8 pan with parchment paper, then set aside.
In a medium mixing bowl, whisk flour, powdered sugar and salt well. Pour in the melted butter and mix with a spoon. The mixture will be crumbly. Use your hands to mix completely if needed, and then using your hands spread the shortbread crust into prepared baking dish. Flatten it down into an even layer. Bake 15-20 minutes until edges are lightly golden.
Filling
While the crust is baking, make the filling. In a mixing bowl, combine lemon zest, lemon juice, water, condensed milk and salt. Mix until completely combined.
Lastly whisk in the cornstarch, until mixed well and no lumps remain. **Add one drop of yellow food coloring to enhance color- optional step but keep in mind the lack of eggs mean there is less yellow coloring Pour filling on top of baked shortbread crust, and bake in oven for another 12-15 minutes, until set. It will be slightly wobbly still but will continue to firm up as it cools.
Allow to cool completely before cutting into the lemon bars. Sprinkle with a bit of sifted powdered sugar if desired.Leave at room temperature for the first day, then refrigerate leftovers for up to 3 days.
