• Preheat oven to 350° F with a rack in the middle position. Lightly grease an 8x8-inch square baking dish.

Make the Apple Filling

• In a large bowl, combine all of the apple filling ingredients: apples, flour, ¼ cup brown sugar, granulated sugar, vanilla, cinnamon, nutmeg and salt. Stir and then set aside. It's ok if everything is not well combined at this point, because the apples will release some of their juices while you prepare the topping and then you will stir the apple mixture again.
  6 cups (2.75 pounds) peeled Granny Smith apples, sliced or chopped (no more than ¼-inch thick)*, ¼ cup all-purpose flour, ¼ cup packed brown sugar, 2 tablespoons granulated sugar, 1 teaspoon vanilla extract, 1 teaspoon ground cinnamon, ¼ teaspoon ground nutmeg, ¼ teaspoon salt

Make the Crisp Topping

• In another large bowl, stir together the oats, flour, ⅓ cup brown sugar, cinnamon and salt.
  1 cup old-fashioned oats, ½ cup all-purpose flour, ⅓ cup packed brown sugar, 1 teaspoon ground cinnamon, ¼ teaspoon salt
• Add the cold butter cubes to the bowl. Use a pastry blender or your hands to work the butter into the oat mixture, until the largest pieces of butter are the size of peas.
  ½ cup cold unsalted butter

Assemble the Apple Crisp

• Stir the apple mixture again until everything is well combined. Pour the apples and all of the juices from the bowl into the prepared baking dish. Sprinkle on the crisp topping.
• Bake for 40-50 minutes, until the topping is lightly browned and the filling is bubbly on the sides of the baking dish. Serve warm or at room temperature.