Perfect Peach-Blueberry Pandowdy

INGREDIENTS

• 10 tablespoons unsalted butter, cut into small pieces
• 2 tablespoons unsalted butter
• 3 tablespoons light brown sugar
• FOR TOP OF CRUST
• 4 cups of pitted, peeled, and sliced ripe peaches plus 2 cups of blueberries (or any combination of stone fruit and/or berries), about 6 cups in total
• FOR FILLING
• pinch of salt
• 1 tablespoon freshly squeezed lemon juice
• 1/4 cup stone ground yellow plain cornmeal
• 1 tablespoon turbinado sugar
• 1 1/4 cup unbleached all-purpose flour
• 3 to 6 tablespoons ice water
• Finely grated zest from 1 small lemon (juice reserved for filling)
• Egg white from 1 large egg, lightly beaten
• 1/2 teaspoon kosher salt
• 2 teaspoons cornstarch (or 1 tablespoon for an all-berry version)
• FOR LEMON-CORNMEAL CRUST