2 cups all-purpose flour
3/4 cup powdered sugar
1/8 teaspoon kosher or fine-grained sea salt
8 ounces (2 sticks) unsalted butter, chilled
2 large egg yolks, at room temperature
3 teaspoons pure vanilla extract, divided
1 pound bittersweet chocolate (66 to 72 percent cacao content), finely chopped
1 1/2 cups heavy cream
3 ounces white chocolate (31 to 35 percent cacao content), shaved
Briefly pulse the flour, sugar and salt in work bowl of a food processor fitted with a steel blade. Cut the chilled butter into small pieces and add. Pulse until butter is cut into very tiny pieces, about 30 seconds. Texture will be sandy with very tiny lumps.
In a small bowl, use a fork to beat the egg yolks with 1 teaspoon of the vanilla. With food processor running, pour this mixture through feed tube. Process until dough wraps itself around blade, about 1 minute. Shape dough into a flat disk and wrap tightly in a double layer of plastic wrap. Chill in refrigerator until firm, about 2 hours, before using.
On a smooth, flat surface, roll out pastry dough between sheets of waxed or parchment paper to a large circle 1/4 inch thick. Peel off top piece of paper and gently roll pastry around rolling pin. Place a pizza pan directly under rolling pin and carefully unroll dough onto pan. Trim off any excess dough at outer edge of pan. Use tines of a fork to press around outer edges of dough, forming a design and creating an outer border. Freeze dough for 15 minutes. Center a rack in oven and preheat to 375 F.
Line pastry dough with a large piece of aluminum foil that fits well against bottom and border and fill with tart weights. Bake for 10 minutes. Remove foil and weights, lightly pierce dough with a fork in several places, to release air and prevent it from puffing up, and bake another 12 to 15 minutes until lightly golden and set. Remove pan from oven and transfer to a rack to cool completely.
Place the bittersweet chocolate in a 2-quart, heatproof mixing bowl. Bring the cream to a boil in a 1-quart saucepan over medium heat. Immediately pour hot cream over chopped chocolate and let stand for 30 seconds. Stir together with a heatproof, silicone spatula until completely melted and smooth. Stir in remaining vanilla and blend thoroughly. Cover top of bowl tightly with plastic wrap and chill until thick, but not stiff, about 1 hour.
Beat ganache filling in bowl of an electric stand mixer using flat beater attachment or in a large mixing bowl using a hand-held mixer on medium speed until it holds soft peaks, no longer than 1 minute.
Transfer filling to cooled pizza shell and spread it out evenly with a rubber spatula or small, offset, metal spatula, leaving a 1-inch border of dough all around. Sprinkle the white-chocolate shavings evenly over top of pizza.
Cut wedge-shaped slices of pizza and serve at room temperature. Store lightly covered with waxed paper and tightly wrapped in foil in refrigerator for up to 3 days.
Makes a 12-inch round tart, about 12 to 18 servings.