Preheat the oven to 375°F.
Add apples, sugar, flour, lemon juice, vanilla, and cinnamon to a 9x13-inch pan. Toss to coat the apples evenly.
7-8 apples, 2 Tablespoons granulated sugar, 2 Tablespoons all-purpose flour, 1 Tablespoon lemon juice, 1/2 teaspoon vanilla extract, 1 teaspoon ground cinnamon
In a large bowl, combine the remaining flour, oats, brown sugar, cinnamon and butter using a pastry cutter to cut the softened butter into the other ingredients until they resemble coarse crumbs. Sprinkle over the apple layer.
1 cup all-purpose flour, 1 cup rolled oats, 1 cup brown sugar, 1 teaspoon ground cinnamon, 3/4 cup salted butter
Bake for 35-40 minutes until the apples are tender and the crisp topping is a nice golden brown.