½cup(113g)salted butter, softened to room temperature
¼cup(21g)natural, unsweetened cocoa powder
1large egg yolk
½cup(113g)salted butter, cut into 4-5 pieces
½cup(85g)semisweet or bittersweet chocolate, chopped, (can use good-quality chocolate chips)
Fleur de sel, for sprinkling (optional)
Preheat the oven to 350 degrees F.
For the crust, in the bowl of a stand mixer fitted with the paddle attachment or in a bowl using a handheld electric mixer (or just mixing by hand), combine the butter, powdered sugar, cocoa powder, salt, egg yolk, vanilla and flour. Mix until combined (it may be crumbly but will hold together when pressed).
Crumble the mixture over the bottom of a 9.5- or 10-inch tart pan (can also use a 9-inch pie plate). Press evenly up the sides first all the way around the edges and then press the remaining crust mixture evenly over the bottom.
Place on a baking sheet and bake for 18-20 minutes. Remove from the oven and let cool.
For the caramel, in a heavy bottomed saucepan (important so that the heat conducts evenly!), combine the sugar, water and corn syrup (try not to splash the mixture up on the sides of the pan). Bring the mixture to a simmer over medium heat. Cook for 10-12 minutes, until the mixture is a medium-dark amber color, tilting the pan just slightly every couple of minutes to swirl the mixture - don't swirl or tilt the pan too quickly or get the caramel mixture up high on the sides of the pan. The exact cooking time will depend on how high/low the heat is on the stove.
Immediately remove the pan from the heat and carefully add the butter, cream and vanilla. The hot mixture will bubble vigorously. Stir to combine (don't go too crazy scraping down the sides of the pan).
Pour the caramel over the baked crust. Refrigerate until the caramel is set and no longer warm, 1-2 hours (make sure you set the tart on a really flat surface in the fridge or else it will set up tilted or uneven).
For the ganache, place the chocolate in a small or medium bowl. Heat the cream (in the microwave or on the stove) until simmering. Pour the cream over the chocolate. Let the mixture sit for 1-2 minutes. Stir to combine until the chocolate is glossy and smooth. Spread the ganache evenly over the caramel. Chill until the chocolate is set and is no longer melty/soft. Sprinkle with a tiny bit of fleur de sel, if desired.
Keep refrigerated until serving. For neat, even slices, I run my long chef's knife under hot water, wipe dry and slice (repeating as needed to get clean slices).
Tart Pan: this recipe calls for a 9-inch tart pan, but a 9-inch pie plate should work pretty well (the advantage to the tart pan is the removable bottom which makes presentation and slicing nicer/easier/prettier).