8 tablespoons (1 stick) unsalted butter, room temperature
1/2 cup plus 1 tablespoon confectioner's sugar
1 large egg yolk
3/4 teaspoon pure vanilla extract
1 1/4 cups all-purpose flour, plus more for rolling
1/4 cup unsweetened Dutch-processed cocoa powder
Peanut Butter Filling:
6 tablespoons unsalted butter, room temperature
3/4 cups creamy peanut butter
1/2 cup confectioner's sugar, sifted
2 tablespoons heavy cream
1/2 cup heavy cream
3 1/2 ounces semi-sweet chocolate chips
Maldon Sea Salt
1. Make the tart dough: In the bowl, using a hand mixer or stand-up mixer with the paddle attachment on, cream butter and confectioner's sugar until combined, about 1 minute. Add egg yolk and vanilla, and beat until smooth. Sift in flour and cocoa powder, and beat on low speed until just combined. Scrape the dough onto a sheet of plastic wrap, and form it into a disk; wrap well in plastic wrap. Chill until firm, at least 1 hour and up to 3 days.
2. Preheat oven to 325 degrees. Between two sheets of lightly floured parchment paper, roll the tart dough into an 14-inch circle. Gently transfer dough to a 9 1/2-inch tart pan. Press the dough into the tart pan, trimming away any excess dough. Chill the tart shell in the refrigerator for 20 minutes.
3. Line the tart shell with a piece of parchment paper or foil, and fill with pie weights (or raw rice or dried lentils). Bake for 15 minutes. Remove the parchment paper and its contents, and bake until the pastry looks dry and set, 5 to 10 minutes. Transfer pan to a wire rack to cool. (The tart shell can be made up to 8 hours ahead.)
4. Make the filling: In a bowl, add the room temperature butter, peanut butter, confectioner's sugar and two tablespoons of heavy whipping cream and mix until smooth.
5. To the chilled tart shell, add the peanut butter mixture and, using a butter knife, smooth out the top. Transfer the filled tart shell to the fridge for 30 minutes to set.
6. Meanwhile, make the ganache glaze: Place the chocolate chips in a heatproof bowl. In a small saucepan, bring cream to a boil. Pour the hot cream over the chocolate, and let stand for 2 minutes, then stir with a rubber spatula until smooth. Pour some of the glaze over the tart while still warm. You can let the glaze set at room temperature for at least 2 hours OR (since I was experiencing a heat wave) transfer the tart to the fridge and allow to set for 30 minutes. Top with a few sprinkles of sea salt and serve.