Instructions

• Position a rack in the middle of the oven and heat to 350°F (175°C). Lightly grease the bottom and sides of a 9½-inch tart pan with a removable bottom.
• In a large bowl, use an electric mixer to beat ½ cup (1 stick) unsalted butter (room temperature), ½ cup firmly packed dark brown sugar, and ¼ teaspoon salt on medium speed until well blended, about 1–2 minutes.
• Add 1 large egg yolk and ½ teaspoon vanilla extract and beat just until combined.
• Reduce mixer speed to low and add 1 cup all-purpose flour. Mix until the dough begins to clump together and holds when pressed, about 30–45 seconds. Do not overmix.
• Scrape the dough into the prepared tart pan. Using lightly floured fingertips if the dough is sticky, gently pat the dough into an even layer on the bottom only (do not press up the sides). Smooth the surface so the layer is uniform.
• Bake on the middle rack until the top looks dry and the dough begins to pull away slightly from the sides of the pan, 25–27 minutes. Remove from the oven and transfer the pan to a wire rack.
• While the crust bakes, place 5 ounces bittersweet or semisweet chocolate (chopped) and 3 tablespoons heavy whipping cream in a heatproof bowl. Melt together using a double boiler or in the microwave in 30-second bursts, stirring well after each burst, until the mixture is smooth and glossy.
• Pour the warm chocolate ganache over the warm crust and spread evenly, leaving about a ½-inch border around the edge. An offset spatula or the back of a spoon works well.
• Immediately scatter ½ cup packaged toffee pieces evenly over the ganache and gently press them into the chocolate so they adhere.
• Let the tart cool completely until the chocolate is fully set: about 4 hours at room temperature or about 2 hours in the refrigerator.
• Once set, remove the outer ring of the tart pan. Use a sharp knife to cut the tart into 16 wedges.
• Serve the chocolate toffee wedges chilled or at room temperature.