Kate’s Peach Berry Sonker by Kate McDermott | Salt + Spine Recipe

Name: Kate’s Peach Berry Sonker by Kate McDermott | Salt + Spine Recipe
Cuisine: American
Ingredients: DOUGH; 1 cup (224 g) butter, cold and cut into tablespoon-size pieces, plus more to butter the baking dish; 2½ cups (363 g) flour; 1 tablespoon aluminum-free baking powder; ½ teaspoon salt; 1 cup (236 ml) milk; 2½ tablespoons flour; 1¼ cups plus 2 tablespoons (275 g) granulated sugar, divided; 4 to 5 cups (1 very generous qt, 1 L) peaches; 3 cups (about 700 ml) blackberries; 1 tablespoon vanilla extract; 5 tablespoons butter; 2 tablespoons sparkling sugar or demerara sugar; 1 egg white plus 2 teaspoons water, fork beaten (or other wash of your choice; see Washes for the Top, Pie Camp page 90); 2½ teaspoons cornstarch; ¼ cup (50 g) plus 2 tablespoons granulated sugar; Pinch of salt; 1½ cups (354 ml) milk; 1 teaspoon vanilla extract