For the filling:
10 to 12 medium-sized apples (I use a mix of Fuji and Granny Smith)
6 tablespoons granulated sugar
3 teaspoons ground cinnamon
For the topping:
22⁄3 cups all-purpose flour
22⁄3 cups packed brown sugar
1 teaspoon ground cinnamon
11⁄3 cups chopped pecans
2⁄3 cup quick-cooking oats
1 cup (2 sticks) unsalted butter, softened
Place a rack in the center of the oven and preheat to 350 degrees F. Grease a 9x13-inch pan with nonstick cooking spray or butter.
To make the filling: peel and core the apples and cut into 1⁄4-inch-thick slices. In a small bowl, mix together granulated sugar and cinnamon. Place all of the apple slices in the baking dish, and sprinkle with the cinnamon sugar mixture. Using your hands, toss the apples with the cinnamon sugar until evenly coated. Set aside while you prepare the topping.
To make the topping: in a medium bowl, whisk together flour, brown sugar, cinnamon, nuts, and oats. Work the softened butter into the dry ingredients with your fingertips until the mixture resembles coarse meal. Remove 1 heaping cup of the topping, and sprinkle it over the apple mixture. Toss with your hands to incorporate. Place apple mixture in the prepared pan and spread the rest of the topping evenly over the apples.
Bake the crisp until topping is toasted and apples are bubbling, 55 to 60 minutes. Remove from the oven and let cool slightly. Scoop warm crisp into bowls and top with vanilla ice cream. You'll thank me. I'm sure of it.