Meanwhile, make the filling
In a large, heavy saucepan, combine the whole eggs, egg yolks, sugar, lemon juice and salt and whisk until smooth. Set a strainer over a bowl near the stove. Cook the custard over moderate heat, whisking constantly, until thickened enough to coat the back of a spoon, about 3 minutes. Remove from the heat and add the butter a few pieces at a time, gently whisking until incorporated. Immediately strain the filling into the bowl. Scrape the filling into the cooled tart shell and refrigerate until chilled, about 2 hours.