Peach Blueberry Cake

INGREDIENTS

• 1 tablespoon quick-cooking tapioca
• 1 teaspoon vanilla
• 1/2 cup sugar
• 1/4 teaspoon salt
• 1 tablespoon fresh lemon juice
• 1 cup blueberries (1/2 pint)
• 2 tablespoons all-purpose flour
• 2 lb firm-ripe large peaches (about 4), halved lengthwise, pitted, and each half cut lengthwise into fourths
• 1 stick (1/2 cup) cold unsalted butter, cut into 1/2-inch cubes
• 1 1/2 cups all-purpose flour
• 1 teaspoon baking powder
• 1 large egg