Preheat oven to 400 F. Lightly grease a 2 quart baking dish (or 9x9-inch baking dish); set aside.
For the apples, stir together apples, sugar, lemon juice, flour, and apple pie spice in a medium bowl. Set aside while you prepare the topping.
7 cups peeled and cored baking apples, ½ cup granulated sugar, 2 tablespoons fresh lemon juice, 2 tablespoons all-purpose flour, 1 tablespoon apple pie spice
For the topping, whisk together flour, sugar, baking powder, baking soda, cinnamon, and salt in a separate medium bowl.
2 cups all-purpose flour, ⅔ cup granulated sugar, 2 teaspoons baking powder, 1 teaspoon baking soda, ½ teaspoon ground cinnamon, ½ teaspoon salt
Cut butter into flour mixture until it forms large crumbs.
6 tablespoons cold salted butter
Stir buttermilk into crumbs to form dough.
1 ⅓ cups buttermilk
Drop dough evenly over apples, spreading slightly if necessary. The dough will spread a little as it bakes.
Sprinkle sugar over dough.
1 tablespoon raw sugar
Place dish on a rimmed baking sheet.
Bake for about 30-40 minutes, or until the filling is bubbly and the topping is golden brown.
Notes
Apples: It's important to use baking apples so that they don't bake down to mush. Granny Smith and Honeycrisp are two common varieties of baking apple. It's also important to thinly slice the apples so that they cook down and get tender.
Apple pie spice: You can use store bought or homemade apple pie spice in this recipe.
Flour: To properly measure the flour either weigh it or sift or stir to break it up, lightly spoon into a measuring cup, and level. Avoid packing the flour as that will give you heavy, dry topping.