4 slices firm white sandwich bread, torn into pieces
SHORTBREAD CRUST:1 1/2 sticks (3/4 cup) cold butter2 cups all-purpose flour3/4 cup packed light brown sugar1 teaspoon salt
APPLE FILLING:1 1/4 sticks (1/2 cup plus 2 tablespoons) butter2 pounds Gala apples1 cup granulated sugar1/4 cup all-purpose flour1 1/2 teaspoons ground cinnamon
Bread crumbs: Preheat oven to 350 degrees. Grind bread to fine crumbs in a food processor. Spread in a shallow baking pan and toast in middle of oven, stirring once, until golden, about 5 minutes. Leave oven on.
Shortbread Crust: Cut butter into 1/2-inch pieces, then pulse in a food processor with flour, brown sugar and salt until it begins to form small lumps. Sprinkle crust into a 13-by-9-inch baking pan and press evenly onto bottom. Bake in middle of oven until golden, about 20 minutes. Prepare filling while shortbread is baking:
Filling: Melt butter and keep warm. Quarter and core unpeeled apples, then thinly slice. Stir together sugar, flour and cinnamon in a small bowl.
Assemble and bake squares: Sprinkle half of cinnamon-sugar mixture over hot shortbread, then top with apples and sprinkle with remaining cinnamon-sugar mixture. Top with bread crumbs and drizzle all of butter over them. Bake in upper third of oven, pressing down on filling with a metal spatula halfway through baking. Bake until apples are very tender and bread crumbs are golden, 50 minutes to 1 hour total. Cool 20 minutes in pan on a rack. Serve warm. Cover and refrigerate any leftovers for up to 4 days. Bring to room temperature before serving or warm each serving about 20-30 seconds in the microwave oven. Even more delicious served topped with vanilla ice cream.