Makes 8 servings
1 1/3 cups unbleached all-purpose flour
2 tablespoons cornmeal, medium-ground
2 tablespoons granulated sugar
1/4 teaspoon kosher salt
6 tablespoons cold unsalted butter, cut into 1/2-inch pieces
2 tablespoons cold vegetable shortening
1/4 cup ice water
5 peaches (about 2 pounds), halved, pitted and sliced 1/4-inch thick
1/4 cup light brown sugar
2 tablespoons cornstarch
1 tablespoon fresh lemon juice
1/2 teaspoon pure vanilla extract
1/4 teaspoon cinnamon
1/4 teaspoon freshly grated nutmeg
Pinch kosher salt
1 tablespoon unsalted butter, cut into pieces
2 tablespoon heavy cream
2 tablespoons turbinado sugar
2 tablespoons apple jelly, melted (optional)
Pulse the flour, cornmeal, sugar and salt in a food processor until combined. Add the butter and shortening, and pulse until crumbs are the size of peas. Add the water and pulse until the dough is evenly moistened. Transfer the dough to a lightly floured work surface, and shape into a disk. Cover with plastic wrap and refrigerate until chilled, about 30 minutes.
Add the peaches, sugars, cornstarch, lemon juice, vanilla cinnamon, nutmeg and salt to a large bowl, and toss to coat. Let stand for about 30 minutes, until the peaches release their juices.
Preheat the oven to 375 degrees F. Line a rimmed baking sheet with parchment paper.
On a lightly floured work surface, roll out the dough to a 12-inch round. Transfer the dough to the baking sheet. Mound the peaches, with their juices, in the center of the dough, leaving a 2-inch border all around. Fold the edge of the dough up and over the peaches, making pleated border. There should be at least 6 inches of fruit showing in the center of the crostata. Brush the dough liberally with the heavy cream and sprinkle with turbinado sugar.
Bake the crostata until the crust is golden brown and the fruit is bubbling at the edges, 45 to 50 minutes. Brush the apple jelly, if using, over the peaches to add a shine to the fruit. Transfer the baking pan to a wire rack and cool for at least 20 minutes before serving.