Make the dough: Combine the flour, sugar, salt, and lemon zest in a food processor. Add the butter and zap quickly until the mixture resembles coarse crumbs. Add the ice water, 1 tablespoon at a time, and zap until the dough just forms a ball without being too wet or sticky. Remove the dough from the processor and pat it into a flat disk, about 2 inches thick. Wrap it in plastic wrap and refrigerate for at least 30 minutes.
Make the filling: Combine the peaches, blackberries, lemon juice, sugar, and flour in a large mixing bowl. Toss the mixture gently to coat the fruit.
Heat the oven to 365° F.
Remove the dough from the refrigerator. Sprinkle your work surface and a rolling pin lightly with cake flour. Roll the dough out into a 16-inch round, about 1/4-inch thick. If the dough tears, press the edges back together. Transfer the dough to a 12 1/2-inch fluted quiche or tart pan with a removable bottom, allowing the excess to hang over the edges. Spoon the fruit mixture into the dough. Fold in the overhanging edges of the dough, leaving a 6-inch area of fruit exposed in the center. Press the crust into the rim of the fluted pan to form an edge.
Place a heatproof bowl over a saucepan of simmering water (or use a double boiler), and heat the honey in the bowl until it is thin. Add the egg and whisk them together. Brush this mixture liberally over the fruit and crust. Place the tart pan on a baking sheet, and bake for 1 hour and 10 minutes or until the crust is golden brown and fruit is bubbly. Remove it from the oven and let it cool slightly.
Serve the crostata warm or at room temperature, with a dollop of mascarpone or whipped cream with each serving.
Mario Batali counts 25 restaurants, 11 cookbooks, numerous television shows and the 50,000-square-foot Eataly marketplace among his ever-expanding empire of deliciousness. His latest book is "America Farm to Table: Simple, Delicious Recipes Celebrating Local Farmers" (Grand Central Life & Style, 2014).