A pate sucree crust is filled with homemade caramel sauce and whipped milk chocolate mousse, then topped with a drizzle of caramel and milk chocolate curls.
Prepare the Mousse: Place the finely chopped chocolate in a heatproof bowl. Place the heavy cream in a medium saucepan over medium heat and bring to a simmer. Pour the hot cream over the chocolate and let sit for 1 to 2 minutes, then whisk gently until the chocolate is completely melted and the mixture is smooth. Strain through a fine-mesh sieve into a separate container and whisk in the salt. Cover and refrigerate for at least 8 hours, or overnight.
Make the Crust: Using an electric mixer, cream together the butter, sugar and salt on medium speed for 2 to 3 minutes, or until pale and light. Scrape the sides and bottom of the bowl, add the flour, and mix on low speed for 30 seconds, or until the mixture looks like wet sand. Add the egg yolk and mix on low speed for another 30 seconds (the dough will still look crumbly, but if you pinch it between your fingers it should hold together).
Gather the dough together and press into a disk, then wrap tightly with plastic wrap. Refrigerate for at least 1 hour.
Remove the dough from the refrigerator and let soften at room temperature for 30 minutes. Using a rolling pin, bang and flatten the dough into a dish about ½-inch thick. Flour the work surface, and sprinkle the dough with flour. Roll out the dough into a 12-inch circle. (Don't worry if the dough breaks a bit, you can easily patch it once you have lined the pan.)
Roll the dough circle around the rolling pin, then unroll it on top of a 10-inch tart pan. Press the dough well into the bottom and sides of the pan, and use any scraps to patch up tears or missing bits. Make sure the entire interior is well covered with dough, and then press one last time all the way around to ensure any holes have been patched. Trim the edge of the dough so it is even with the rim of the pan (I always run my rolling pin across the top, which creates a flush top with the pan!). Refrigerate for at least 30 minutes. (The pastry shell can be tightly wrapped in plastic wrap and refrigerated for up to 1 day or frozen for up to 2 weeks. Bake directly from the refrigerator or freezer.)
Preheat oven to 350 degrees F. Bake for 30 to 35 minutes, or until golden brown. Place on a wire rack and cool to room temperature, the unmold the tart from the ring.
Finish the Mousse: Using a stand or handheld mixer with a whisk attachment, whip the chocolate-cream mixture on medium-high speed until it holds firm peaks.
Assemble the Tart: Spread the caramel sauce evenly in the bottom of the tart shell, then spread the whipped chocolate evenly over the caramel layer. Drizzle with a couple spoonfuls of caramel sauce, and top with chocolate curls, if desired. Refrigerate for at least 30 minutes before serving. The tart should be served within 1 day of assembling.
Notes
The pate sucree dough can be stored in the refrigerator for up to 5 days or in the freezer for up to 2 weeks. If frozen, thaw it in the refrigerator overnight before using.
I like using the salted caramel sauce because it cuts some of the sweetness, but you can certainly make it without the fleur de sel for a more traditional caramel sauce.