1In a stand mixer fitted with a paddle attachment, combine the flour, sugar, salt and orange zest and mix for 30 seconds. Scrape in the vanilla seeds and add the chilled butter. Mix at medium speed for 3 to 5 minutes, or until the mixture looks like coarse crumbs.
2In a small bowl, beat the egg yolks with 1/4 cup of the grappa, then add it to the dough mixture and mix for 30 seconds to 1 minute, until the dough begins to detach from the sides of the bowl.
3Transfer the dough to a work surface and shape it it into a disc. Cover it with plastic wrap and refrigerate it for at least 1 hour.
4Preheat the oven to 425 Fº. Grease an 11-inch tart pan with a removable bottom with butter.
5In a small bowl, combine the jam and remaining 3 tablespoons of grappa, mixing well.
6On a floured surface, roll the dough to about 1/8 inch thick, and gently lay it into the tart pan. Press the dough lightly against the sides. Using your fingers, press on the dough against the rim of the pan to cut off excess dough.
7Using a fork, poke the dough all the way through to the pan surface several times (this will allow the oven’s hot air to come through).
8Using a spoon, spread the jam on top of the dough.
9Bake the tart for 25 minutes, until golden brown. Remove from the oven, let cool, and serve.