1 cup (2 sticks) unsalted butter
2 ⅔ cups all-purpose flour
5 tbsp. confectioners’ sugar
½ tsp. salt
⅔ cup ice water
½ pound ripe black plums, unpeeled
½ pound firm ripe peaches, peeled
½ pint fresh raspberries
½ pint fresh blackberries
1 tbsp. unsalted butter, melted
2 tbsp. granulated sugar
Cut the butter into ½ inch pieces, place on a plate, and chill in the freezer for 10 minutes.
Meanwhile, combine the flour, confectioners’ sugar, and salt a food processor. Pulse to blend. Add the butter pieces and pulse 3 or 4 times for about 4 seconds each, just until the mixture looks like very coarse bread crumbs (the butter should be in pea-sized pieces). Add the ice water and pulse for 5 to 10 seconds until the dough just comes together. Streaks of pure butter in the dough are okay. Turn the dough out onto a lightly floured board, press into a thick disk, and wrap in plastic. Refrigerate for at least 1 hour or overnight. If chilled for more than 1 hour, let the dough stand for 10 to 30 minutes before rolling out.
Preheat the oven to 400 degrees F and place a rack in the center.
Place a sheet of parchment paper on a work surface and dust generously with flour. Place the dough in the center and roll it out into a large rectangle, approximately 15” x 20”; don’t worry if the edges are rough and uneven. Slide the parchment onto a baking sheet.
Brush the preserves over the dough, leaving a 2” border. Arrange the plums and peaches over the preserves in concentric circles overlapping the slightly. Spread raspberries and blackberries evenly. Lift the edges of the dough and fold them in over the fruit, pinching the dough into pleats as you fold. Brush the top of the dough with the melted butter and sprinkle the granulated sugar over the whole tart. Bake for about 35 minutes, until the crust is bubbling and browned and the plums are bubbling tender. Slide the tart from the parchment onto a rack and cool for 10 minutes. Serve, cut in wedges, warm or at room temperature.