Summer-Fruit Cobbler

Heat oven to 375 °F. Butter a 9"-square baking pan. In a bowl, toss nectarines and raspberries with 1/3 cup granulated sugar, cornstarch, juice and 1/4 teaspoon salt to combine; add to pan. In another bowl, whisk remaining 1/3 cup granulated sugar, flour, cornmeal, baking powder, baking soda and remaining 1/2 teaspoon salt. In a food processor, pulse sugar-flour mixture 10 seconds; add sliced butter; pulse until dough pieces are the size of peas, 1 minute. Add buttermilk; pulse a few more times until just combined. Use a 1/3-cup measure to portion dough into 10 round biscuits; place on top of fruit. Lightly press biscuits with fingers to flatten tops; sprinkle cobbler with raw sugar. Bake until juices bubble thickly and biscuits are golden brown, 50 minutes. Serve warm or at room temperature.