Caramel Chocolate Truffle Tart

Name: Caramel Chocolate Truffle Tart
Ingredients: 1 large egg yolk; 2 tablespoons heavy cream; 1/2 teaspoon vanilla extract; 1 1/4 cup unbleached all-purpose flour (6 1/4 ounces/177 grams); 1/4 cup Dutch-processed cocoa powder (3/4 ounce/21 grams); 3/4 cup Confectioners' sugar (3 ounces/85 grams); 1/4 teaspoon salt; 10 tablespoons cold unsalted butter , cut into 1/2-inch cubes; 1/4 cup water; 1/2 cup sugar; 1/2 cup heavy cream; 1/4 teaspoon vanilla extract; 1/4 teaspoon juice from 1 lemon; Pinch salt; 2 tablespoons butter; 12 ounces (340 grams) high-quality bittersweet chocolate , chopped; 1 cup heavy cream; 6 tablespoons (3/4 stick) unsalted butter , at room temperature; 1 tablespoon Cognac