Step 1

Preheat oven to 350°. In a large bowl, combine flour, oats, brown sugar and baking soda; cut in 1 cup plus 2 tablespoons butter until mixture resembles coarse crumbs. Set aside 2 cups for topping. Press remaining oat mixture into a greased 13x9-in. baking pan. Arrange apples over the top.

Step 2

In a small saucepan, combine sugar, cornstarch, water, vanilla and remaining 2 tablespoons butter. Bring to a boil. Cook and stir until thickened, 1-2 minutes; pour over apples. Sprinkle with reserved oat mixture.

Step 3

Bake until top is lightly browned, 35-45 minutes. Cool in pan on a wire rack. If desired, serve with vanilla ice cream.