Lower the oven temperature to 350ºF.
Combine the sugar and lemon zest in a small bowl and massage together, making sugar very fragrant.
Pour the sugar into a 2-quart saucepan. Add the lemon juice, eggs, egg yolks and salt and whisk to combine. Cook over medium heat so mixture is warmed through. Add the butter gradually and stir until all the butter has melted. Continue cooking over medium heat until mixture is thick enough to coat a spatula, 5 to 8 minutes, stirring frequently and scraping the corners of the saucepan. Remove from the heat and strain the curd through a fine-mesh-sieve.
Keep the baked tart crust in the tart pan on its baking sheet. Pour the curd into the tart crust and smooth the surface using an offset spatula.
Bake the tart for 5 to 10 minutes, just to set the filling. The edges should be solid while the center retains the slightest of jiggles.
Cool completely before adding meringue.