Preheat oven to 350 degrees F. Line a 13-in. x 9-in. baking dish with parchment paper and spray lightly with nonstick cooking spray.
In a large bowl, combine flour, oats, brown sugar, baking soda and salt. Cut in 1 cup plus 2 tablespoons butter until mixture resembles coarse crumbs. Set aside 2 cups for topping.
Press remaining crumbs into prepared baking dish. Evenly arrange apples over top.
In a small saucepan, combine sugar, cornstarch, water, vanilla, cinnamon, nutmeg and remaining 2 Tablespoons butter. Bring to a boil. Cook and stir for 2 minutes or until thick and bubbly; spread over apples. Sprinkle with reserved crumbs.
Bake for 35-45 minutes, or until top is lightly browned. Let bars cool completely before cutting.
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