Making the dough:
Put the flour, sugar, and salt in the bowl of a food processor fitted with the metal blade, and process for a few seconds to mix the dry ingredients.
Cut the butter into 1/2-inch pieces, drop them onto the flour, and pulse the machine ten or twelve times, in short bursts, 20 seconds in all. The mixture should be crumbly, with only a few larger bits of butter visible.
Sprinkle 3 tablespoons of water on top of the dough; immediately pulse about six times, only a second or two each time. You want the crumbs to gether together in wet clusters, a bit like cottage-cheese curds--don't expect a mass of dough to form. if they haven't gathered, sprinkle on ore water, a teaspoon at a time, and pulse two or three times after each.
When the clusters form, scrape them all out of the bowl, press them together, and knead just for a few seconds to form a smooth, tight dough. Flatten it into a disk, wrap well in plastic wrap, and refrigerate for 3 hours or up to a day before using. Freeze the dough for longer keeping.
(If the crumbs haven't clustered after you've added 4 tablespoons of water, open the top and press them with your fingers; if they're wet and stick together, just empty the bowl and press them into a disk of dough.)
Making the filling and rolling the dough:
Arrange a rack in the middle of the oven with a baking stone on it, if you have one. Preheat the oven to 375°. If the crostata dough is very cold, let it soften at room temperature for a few minutes while you make the filling.
Rinse the plums and pat dry. Cut them in flat halves, following the natural line around the fruit through the stem end, and remove the pits. Toss the halves with the lemon zest, apricot jam, and butter bits in a mixing bowl. (If you’re making the crostata with large plums or fruit like peaches or nectarines, cut in quarters or wedges.)
Toss the bread crumbs, sugar, and cinnamon together.
On a lightly floured board, start stretching the dough into a circle, rolling from the center in all directions. Turn the dough over as it stretches, and flour the work surface as needed.
Cut a piece of parchment that will cover your baking sheet. Roll the circle of dough to a diameter of 15 inches, and lay it, centered, on the parchment. Now trim the outside edges of the dough, with a sharp knife or scissors, cutting away ragged or thin spots and making as perfect a round as you can, since this edge will be visible on the top of your crostata. Keep the circle at least 13 inches in diameter. Lift the parchment with the dough on it to the baking sheet.
Filling and baking the crostata:
Sprinkle about 1/3 cup of the bread-crumb mix in a 7-to-9-inchdiameter circle in the center of the dough, as a base for the fruit. The bread crumbs will soak up the juices, so if you have very ripe and juicy fruit (like peaches) use more crumbs, to form a thicker layer; if using a drier fruit, like apricots, use less crumbs.
Arrange the coated plum halves, cut side up, on top of the crumb base. I place them in concentric rings, starting from the outside, and lean each inner ring on the plums just outside. In this manner, with a larger, 8- or 9-inch base of crumbs, you should be able to fit all the plums in one layer, for a crostata with an even height. If the crumb base is smaller, you’ll need to pile up the fruit. This will give the crostata more of a dome shape.
When you’ve assembled your fruit in the middle of the dough, fold the uncovered band of pastry on top of the fruit. The width of the band will vary with your arrangement of the plums, but you should have at least 2½ inches of dough to form the pleated top crust.
Finally, sprinkle 1 or more tablespoons of sugared bread crumbs over the visible fruit in the center. As before, use more crumbs on juicy fruit. If you have any left over, sprinkle them over the pleated dough.
Put the baking sheet with the crostata in the oven, on the stone if using one, and bake for 25 minutes; rotate the pan back to front for even cooking. Continue baking, and check the browning of the crust after 40 minutes: it should be light gold. If it is getting quite dark, you may need to lay a piece of foil on top. Bake for another 15 minutes or more, until the fruit is bubbling and has caramelized on the edges. If you’ve filled the crostata with a mound of fruit, you’ll probably want to bake it more than an hour—and cover the top—to make sure all the fruit is cooked.
Let the crostata cool on the baking sheet for about 15 minutes or more before lifting it, with the parchment, to a wire rack to continue cooling. When it has set, slide it off the parchment, supported by long spatulas, onto a platter.
Serve warm or at room temperature, cut into wedges, with whipped cream or vanilla ice cream, if you wish.
