Ingredients

• 1/2 cup + 1 T / 4.5 oz / 130g unsalted butter, room temperature
• 1/2 cup / 2.5 oz / 75g natural cane sugar, muscovado, or brown sugar, sifted
• 1/4 teaspoon fine grain sea salt
• 1 large egg, room temperature
• 1 3/4 cup / 8 oz / 225g whole wheat pastry flour
• scant cup / 225 ml heavy whipping cream
• 2 tablespoons milk
• 7 ounces / 200g 70% bittersweet chocolate, chopped
• 1 large egg, beaten
• flaky sea salt, cocoa powder

Directions

1. Start by making the tart dough. Use an electric mixer with the paddle attachment to cream the butter, sugar and salt until well combined. Alternately, you can do this by hand. Add the egg and mix until smooth. Use a spatula to scrape down the sides of the bowl a couple times along the way. Add the flour and pulse the mixer on and off, low speed, until the dough comes together and has a moist appearance. Divide the dough into two equal pieces, shape each into a ball, press into 1/2-inch thick disks, and wrap in plastic, or place in baggies. Chill for at least an hour.
2. Preheat the oven to 350F / 180C. Place a rack in the middle of the oven.
3. When you are ready to line the tart pans with dough, place one of the dough disks on a lightly floured surface and roll out until the dough is large enough to line your tart pan. I usually eyeball it - you can see in the photo the dough is about 1/6 - 1/8 inch thick. Dust underneath with flour to discourage sticking throughout the rolling process. Carefully transfer the dough to the pan. Don't worry too much if you get a tear or hole, you can patch those up later with scraps. Work quickly to ease the dough into place, taking care not to stretch the dough. Press it along the bottom of the pan, out to the walls, and against the sides. Trim any excess dough - I use the palm of my hand against the edge of the tart pan to cut off any extra dough, alternately you can roll a rolling pin across the rim of the pan for a clean edge. It should look like the second photo up above. Chill in the refrigerator for thirty minutes more while you roll out your extra tart shell. Double wrap that one in plastic and freeze it for future use.
4. You're going to partially bake the tart shell before filling it, so pull the shell out of the refrigerator, dock it with a fork, making small holes along the bottom of the shell - see photo. Line the shell with parchment paper and fill to the rim with pie weights or dried beans, bake for 10 minutes. Carefully remove the pie weights and finish baking for another 6 - 8 minutes, or until the crust is dry and just barely starting to brown. Remove from oven and let cool completely.
5. Make the chocolate filling by bringing the cream and milk to a gentle simmer in a saucepan over medium heat. Remove from heat, add the chocolate, and stir until the chocolate is melted and the mixture smooth. Let cool five minutes, add the egg, and whisk until completely blended. If the chocolate is too hot, you're going to scramble the egg, be cautious.
6. Pour the filling into the cooled tart shell and bake for about 15 minutes, give or take a couple minutes. The filling should be set around the edges a bit darker than the center in color. The center will be a touch jiggly, that's o.k. I baked this tart in a slightly smaller/deeper tart pan and it took longer than its wider, shallower 9-inch counterpart. Just keep an eye on things.
7. Let the tart cool completely, preferably in the pan on a cooling rack. Dust with a bit of cocoa powder, and sprinkle with touch of flakey sea salt. You can serve at room temperature or chilled - it's easier to slice when it's chilled.
8. Serves 8 - 10.