The recipe is straight out of my cookbook, except I'm substituting a potentially easier way to make the crust. Have at it!
1 cup all-purpose flour
1/4 cup granulated sugar
2 tablespoons cocoa powder
1/4 teaspoon salt
1/2 cup cold unsalted butter (1 stick), cut into 8 pieces
1 to 2 tablespoons milk
Few drops of vanilla
1-1/3 cups bittersweet chopped chocolate or chocolate chips
3 tablespoons granulated sugar
1/4 teaspoon salt
1 tablespoon Chambord or crème de cassis (optional)
1-1/4 cup heavy cream
2 tablespoons unsalted butter
1 to 2 pinches large, coarse-grained sea salt, like Maldon or Fleur de Sel
2 tablespoons finely chopped pistachios (optional)
For the crust, add the flour, sugar, cocoa powder, and salt to the bowl of a food processor and pulse to combine. Add the butter pieces and pulse in 1-second beats until you have chunks of butter the size of peas, 8 to 10 pulses. Add 1 tablespoon of milk with a few drops of vanilla through the feed tube, and pulse until the dough starts to clump. If it doesn't clump after 12 pulses, dribble in the remaining tablespoon of milk a little at a time, pulsing the motor after each addition, until the mixture clumps together. (You can also cut the butter into the dry ingredients with an electric mixer, a pastry blender, or your fingers. Add the milk in increments, fluffing with a fork, until the dough holds together when pressed.) Dump the dough onto the counter and form it into a ball. Flatten it into a disk about 3/4-inch thick and wrap it in plastic wrap. Let the dough rest in the refrigerator for 30 minutes.
Preheat the oven to 350°F. Roll out the dough on a well-floured surface into a circle about 1/4-inch thick and 12 inches in diameter. With a bench scraper or spatula, flip one side of the dough over the top of the rolling pin, gently loosening the dough if it sticks to the counter, until it is fully draped over the pin. Center the dough over a 10-inch tart pan and unfurl. Gently fit the dough into the corners of the pan without stretching it. Clip off the excess dough by rolling the pin over the top. Gently press the dough against the sides of the pan with your fingers so the dough level rises slightly above the pan's edge to compensate for shrinkage. Use the scraps to reinforce any areas that are too thin. Poke the bottom crust with a fork about a dozen times. Line the dough with aluminum foil. Fill with pie weights all the way to the sides to keep the dough from shrinking (dried beans or rice work well). Bake the crust for 20 minutes, and then carefully remove the foil and weights. Bake for 10 to 15 minutes more, or until the bottom crust is cooked and dry. Let it cool completely before filling.
For the filling, combine the chocolate, sugar, salt, and Chambord in a medium bowl. In a small saucepan, heat the cream and butter until the butter has melted and the cream is hot with some bubbles forming around the edges. Do not boil. Pour the cream mixture over the chocolate and let it sit for 1 minute. Gently whisk just until smooth so as not to create air bubbles. Pour the filling into the tart shell and set it on an even surface in the refrigerator for at least 6 hours, or until firm.
Just before serving, sprinkle the tart with sea salt, or ground pistachios, or both! The tart can be stored covered in the refrigerator for 1 to 2 days, but the salt will start to break down (totally edible, just not as pretty).
Source: Adapted from WINTERSWEET by Tammy Donroe Inman.