Mulberry trees are closely associated with the French silk industry. Thousands of trees were planted to succor the worms that eat the leaves and spin silk threads. The silk industry declined in the 1800s, but the mulberry trees remain. In Provence, they are pruned each winter to force the long branches, which are attached to lateral wires, to provide a dense shade canopy. Many homes and restaurants have them planted just for this reason. The small, elongated berry-like fruits can be purple, pink, or white, and sweetness varies. Their season is short, and any fresh berries can be substituted here. The pistachios add both crunch and color to the shortbread crust. I suggest purchasing the nuts in the shell, as they tend to retain their texture better than shelled nuts.
WHAT YOU NEED
For the Pastry
1 cup (4 oz/125 g) pistachios in the shell
¼ cup (2 oz/60 g) plus 2 Tbsp sugar
1 ½ cups (7 ½ oz/235 g) all-purpose flour
4 Tbsp (2 oz/60 g) cold unsalted butter, cut into ½-inch (12-mm) chunks
1 large egg
For the Pastry Cream
1 cup (8 fl oz/250 ml) whole milk, plus milk as needed
½ cup (4 oz/125 g) sugar
3 large egg yolks
⅓ cup (2 oz/60 g) all-purpose flour
1 Tbsp unsalted butter, at room temperature
1-inch (2.5-cm) piece vanilla bean, split lengthwise
For the Berry Topping
3 cups (14 oz/430 g) fresh mulberries
1 ½ Tbsp sugar
Juice of 1 lemon
For the whipped cream (optional)
½ cup (4 fl oz/125 ml) heavy cream
1 Tbsp sugar
WHAT TO DO
Preheat the oven to 180°C (350°F).
To make the pastry, shell the pistachios. You should have about ½ cup (60 g). Use a mortar and pestle, clean coffee grinder, or small food processor to grind together the pistachios and 2 tablespoons of the sugar until the nuts are coarsely ground. You may need to work in batches. Some of the pistachios will be finely ground, others chunkier. Set aside.
In a bowl, stir together the flour and the remaining ¼ cup (60 g) sugar. Add the butter and work it in with your fingers or a pastry cutter until crumbly and the size of peas. Add the egg and mix it with a fork. Tightly pack the dough into a ball. Using your fingers, press the dough evenly into the bottom and up the sides of a 9-inch (23-cm) fluted tart pan with a removable bottom. Sprinkle half of the pistachio-sugar mixture over the pastry and gently press it in.
Bake until the crust turns lightly golden and pulls away slightly from the sides of the pan, 15–20 minutes. Set aside to cool.
To make the pastry cream, in a saucepan, heat the milk over medium-high heat just until fine bubbles form around the edges, about 2 minutes. Do not boil.
In a bowl, using an electric beater, beat together the sugar and egg yolks until the mixture is a light lemon color, about 2 minutes. Beat in the flour to form a thick paste, about 1 minute longer.
Gradually pour the hot milk into the sugar mixture, beating continuously. When the milk has been thoroughly incorporated, pour the mixture back into the saucepan, bring to a boil over medium-high heat, and cook, beating continuously, until the mixture thickens, 1–2 minutes. Immediately remove from the heat and whisk vigorously until very thick, about 1 minute. Whisk in the butter and scrape the vanilla seeds into the pastry cream.
Let cool slightly. If the pastry cream seems too thick to spread, add up to 1 tablespoon more milk. Pour the pastry cream evenly into the pastry shell, smoothing the top.
To prepare the berry topping, in a large bowl, gently toss together the mulberries, sugar, and lemon juice. If serving the tart with whipped cream, set aside about 16 mulberries for garnishing the cream.
Lay the mulberries on the pastry cream, heaping them a bit in the middle. Sprinkle with the remaining pistachio-sugar mixture. (If not serving right away, cover loosely with plastic wrap or aluminum foil and refrigerate. Let stand at room temperature for 10–15 minutes before serving.)
Slip a knife around the edges of the pan to loosen any clinging bits of pastry. Gently push on the bottom of the pan, nudging the ring loose. Slide the tart onto a serving plate.
If serving the tart with whipped cream, pour the cream into a bowl and, using the electric beater, whip the cream until it starts to thicken. Add the sugar and continue to beat until stiff peaks form.
Cut the tart into wedges. Top each serving with a dollop of whipped cream, if using, and top the cream with a mulberry or two. Serve at once.