Pasta frolla:Place sugar, flour, salt, and lemon zest in a food processor and pulse several times to mix well.Add butter and pulse until mixture has a coarse texture.Add egg yolks and egg, and pulse just enough to form a ball of dough.Let it rest for 30 minutes in the refrigerator, wrapped in plastic film.Butter a 9″ (23cm) diameter and 1 1/2″ (4cm) high tart mold well.Divide dough into 2/3 and 1/3.Roll out 2/3 of the dough and place it in the mold, pressing it against the sides.Reserve the prepared dough in the refrigerator while preparing the rest of the recipe.Roll out the remaining 1/3 of the dough and cut into 1/2″ (1cm) wide strips.Reserve them in the refrigerator as well.Filling:Heat the milk with the split and scraped vanilla pod.In a bowl, mix sugar, egg yolks, and flour.Gradually dilute with warm milk, then put everything back in the saucepan.Bring the mixture to a boil, stirring constantly, until it thickens.Remove the vanilla pod and let cool.Assembly and baking:When the pastry cream is cool, pour it into the reserved tart mold.Spread the apricot jam, then arrange the strips of dough in a lattice pattern.Form a border around the tart with a long strip to hold the lattice in place.Lightly brush the border and the strips of dough with beaten egg.Preheat the oven to 350°F (180°C) and bake the tart for 35 minutes or until the lattice is golden brown.Remove from the oven and let it cool completely in the mold before cutting and serving.