For the dough:
1½ cups all-purpose flour
¾ cup confectioners’ sugar
½ cup Dutch-process cocoa powder
Pinch of salt
12 tbsp. (6 oz.) cold unsalted butter, cubed
1 large egg yolk, lightly beaten
1 tbsp. vanilla extract
2 tbsp. heavy cream
For the caramel layers:
12 oz. soft caramel candies, unwrapped, divided*
2½ tbsp. heavy cream, divided
For the chocolate filling:
8 oz. bittersweet chocolate, finely chopped
¾ cup heavy cream
1 tbsp. light corn syrup
2 tbsp. unsalted butter, at room temperature
To make the dough, combine the flour, confectioners’ sugar, cocoa powder and salt in a medium bowl; stir with a fork to blend. Add the cubes of butter to the bowl with the dry ingredients. Cut the butter into the dry ingredients using a pastry blender or two knives until the mixture resembles coarse meal and small pieces of butter remain. Add in the egg yolk, vanilla and heavy cream, and stir with a fork until a dough comes together. Knead very briefly, handling as little as possible, until the dough has an even consistency. Form into a disc, cover with plastic wrap, and refrigerate until firm, at least 1 hour.
Preheat the oven to 400˚ F. On a lightly floured surface, roll the dough out to about ¼-inch thickness or slightly thinner. Cut out rounds large enough to fully line the mini tart pans (pans 4-inches diameter, at least 1 inch high), about 6 inches in diameter. Line the pans with the dough, pressing into the edges of the pans to fill the fluted portions. Trim away the excess dough. Line each crust with a small piece of foil and fill with baking beads (dry rice or beans will also work). Place the tart pans on a baking sheet. Transfer to the oven and bake about 18 minutes, until mostly set. Reduce the oven temperature to 375˚ F, remove the foil and baking beads. Return the tart shells to the oven and bake for 5 minutes more. Transfer the tart shells to a wire rack to cool completely (leave in the pans).
To make the bottom caramel layer, combine 9 ounces of the caramels with 2 tablespoons of the cream in a medium bowl. Microwave in 20-30 second intervals, stirring in between, until the mixture is fully melted and smooth. (Alternatively this can be done in a small saucepan over medium-low heat.) Divide between the tart shells, pouring an even layer to cover the bottom of each shell. Transfer the pans to the refrigerator or freezer and let chill until the caramel layer is set, about 30 minutes.
Place the chocolate in a heatproof bowl. Bring the cream to a simmer in the microwave or a saucepan. Pour the hot cream and the corn syrup over the chopped chocolate and let stand about 2 minutes. Whisk together until a smooth ganache forms. Whisk in the butter until completely incorporated and the mixture is totally smooth. In another small bowl, combine the remaining 3 ounces of caramels and the remaining 1½ teaspoons of cream. Microwave in short intervals (it may only take one) until fully melted and smooth. Divide the chocolate mixture between the tartlet shells, pouring an even layer over the caramel. Immediately top each with three small dots of the caramel. Use a toothpick or skewer to marble in a heart pattern. Refrigerate until fully set, at least 2 hours. Just before serving, sprinkle with coarse sea salt, such as fleur de sel.
*The better the quality of the caramels you use, the better this dessert will taste. I like to make my own caramels and use those. Make them now and have them ready when you want to make the tartlets…assuming they survive that long, of course :)