For the base
1½ cups all-purpose flour
½ cup confectioners’ sugar
¼ teaspoon salt
9 tablespoons very cold or frozen unsalted butter, cut into small pieces
1 large egg yolk
For the filling
8 ounces mascarpone cheese
⅓ cup well-chilled heavy cream
¼ cup sugar
1½ cups strawberries, hulled and halved or quatered
1½ cups blueberries
1½ cups blackberries
2 tablespoons strawberry (or other berry) jam
2 tablespoons dark berry liqueur, like crème de cassis
Fresh mint leaves for garnish, optional
Start by making the crust. Put the flour, confectioners’ sugar and salt in the bowl of a food processor and pulse to combine. Scatter the butter over the top and pulse again until the butter is mixed in with some pea-sized pieces remaining. Whisk the yolk in a small bowl. Drizzle it into the food processor, a little at a time, pulsing after each addition. Continue processing in long pulses until the dough forms clumps and then comes together. Scrape down the sides of the bowl as needed.
Grease a 9-inch fluted tart pan with a removable bottom. Press the dough evenly across the bottom and up the sides of the pan. Freeze for at least 30 minutes before baking.
When ready to bake, heat oven to 375º. Spray a piece of aluminum foil with nonstick spray and place, oil side down, firmly onto the crust. Place the tart pan on a baking sheet and bake for 25 minutes. Carefully remove the foil and use the back of a spoon to gently press down the crust if it has puffed. Continue baking another 8 minutes, until the crust is firm and golden. Transfer to a cooling rack to cool completely.
To make the filling, combine the mascarpone, cream and sugar in a medium bowl. Using an electric mixer, beat until the mixture holds stiff peaks. Transfer the mixture to the cooled shell and use a spatula to smooth it evenly. Refrigerate while preparing the berries.
In a large bowl, combine the strawberries, blueberries and blackberries. Combine the jam and berry liqueur in a small saucepan and bring to a simmer. Cook until reduced to about 3 tablespoons. Pour the mixture over the berries and gently toss to coat evenly. Mound the berries over the top of the mascarpone cream. Garnish with fresh mint, if desired.
The tart can be made a couple hours ahead of time and chilled. It’s best the day it’s made, but that didn’t stop us from enjoying the last remaining slice the next day.