Preheat oven to 300 degrees F. Coat an 8-by-12-inch baking dish with cooking spray.Advertisement
Process graham crackers and cinnamon in a food processor until you have fine crumbs. Leaving about 1/2 cup in the workbowl, transfer the crumbs to another container. Add apples to the workbowl and process until coarsely chopped.
Combine sugar, egg whites, egg, vanilla and salt in a large bowl. Beat with an electric mixer on high speed until thick, about 3 minutes. Fold in the reserved crumbs, apples and the toasted walnuts just until combined. Transfer batter to the prepared baking dish; smooth the top with a wet rubber spatula. Bake until the top feels dry and a skewer inserted in the center comes out clean, 30 to 35 minutes.
Let cool completely on a wire rack. Dust lightly with confectioners' sugar and cut into 15 bars.
Make Ahead Tip: Store in an airtight container for up to 1 week. Freeze for longer storage.
Tip: To toast chopped walnuts: Place in a small dry skillet and cook over medium-low heat, stirring constantly, until fragrant and lightly browned, 2 to 4 minutes.
Storage smarts: For long-term freezer storage, wrap your food in a layer of plastic wrap followed by a layer of foil. The plastic will help prevent freezer burn while the foil will help keep off-odors from seeping into the food.
1 starch, 1/2 other carbohydrate, 1/2 fat