Cut in the butter until the mixture resembles coarse meal.
1/2 cup (114g) unsalted butter
Transfer the mixture to the prepared tart pan. Evenly press the shortbread crust onto the bottom and 1" up the sides of the pan. Bake for 10-15 minutes or until lightly golden.
Meanwhile, in a medium mixing bowl, whisk together the sugar, flour, and salt.
1 cup (200g) granulated sugar, 1/4 cup (30g) all-purpose flour, 1/4 tsp salt
Then whisk in the eggs, lemon zest, and lemon juice.
2 large eggs, zest of 1 lemon, 1/4 cup lemon juice
Pour the filling into the hot crust and place back in the oven for another 20-25 minutes or until the filling is set. Let cool completely before serving.
Optional - beat the whipping cream and powdered sugar to stiff peaks. Pipe along the edge of the tart and decorate with a few lemon slices if desired.
Notes
Leftovers can be covered and stored in the fridge for up to3 days.