In a medium bowl, blend together the sugar and lemon zest with your fingers to release the oils from the zest. The mixture should be damp and very fragrant.
1 ⅓ cup granulated sugar, 1 tablespoon lemon zest
Whisk in the flour and salt until blended.
3 tablespoon all purpose flour, pinch of fine sea salt
Add the eggs and whisk briskly so that the sugar doesn't "cook" the eggs and form clumps.
4 large eggs
Add the lemon juice and cream and whisk to fully incorporate.
⅔ cup lemon juice, freshly squeezed, ⅓ cup heavy cream
Pour the filling over the warm shortbread and bake for an additional 25-30 minutes, until filling looks set and doesn't jiggle.
Let the bars cool to room temperature, about 1 hour. Place in the refrigerator to cool for an additional hour. The longer they cool, the easier and prettier they are to slice.
Transfer bars to a cutting board and cut into squares or wedges. Using a sieve, sprinkle with confectioner's sugar and serve.
confectioners sugar for dusting