Heat the oven to 400 F. Lightly coat a 9-inch square baking dish with cooking spray.

In a large bowl, add the apple slices. Sprinkle with lemon juice. In a small bowl, combine the sugar, cornstarch and cinnamon. Add the mixture to the apples and toss gently to mix. Stir in the blueberries. Spread the apple-blueberry mixture evenly in the prepared baking dish. Set aside.

In another large bowl, combine the flours, sugar, baking powder and salt. Using a fork, cut the cold margarine into the dry ingredients until the mixture resembles coarse crumbs. Add the milk and vanilla. Stir just until a moist dough forms. Turn the dough onto a generously floured work surface and, with floured hands, knead gently 6 to 8 times until the dough is smooth and manageable. Using a rolling pin, roll the dough into a rectangle 1/2-inch thick. Use a cookie cutter to cut out shapes. Cut close together for a minimum of scraps. Gather the scraps and roll out to make more cuts.

Place the dough pieces over the apple-blueberry mixture until the top is covered. Bake until the apples are tender and the topping is golden, about 30 minutes. Serve warm.