Using 5 lbs of Granny Smith apples peel and thinly slice the apples with an end result of 9 cups.
Place all the filling ingredients directly over the raw apples in the baking dish.
Add 1 teaspoon of vanilla and carefully stir until the apples are coated evenly, with no visible patches of flour or sugar.
Gently press the apples down in the pan to even them out.
Cobbler Topping:
In a large mixing bowl, combine the dry ingredients: 2 1/2 cups of flour, 1 1/2 cups of granulated sugar, 1 teaspoon of kosher salt, and 1 teaspoon of baking powder. Give it a good whisk to blend.
In a separate smaller bowl, whisk together 1/2 cup of buttermilk and 1 egg. Pour this mixture into the dry ingredients. Using a pastry cutter (or a spoon or fork if you don’t have one), cut the wet mixture into the flour until you get a rough, shaggy dough. It's fine if there are a few dry spots of flour remaining.
Spoon or pour the dough evenly over the apples in a 9x13-inch baking dish.
Cut a stick of butter into 1/2-inch cubes and distribute them evenly over the top of the flour mixture.
Sprinkle 2 tablespoons of sugar on top for extra crunch. You can use a mix of granulated and demerara (raw) sugar for added texture.
Bake at 375°F for 45-55 minutes, or until the top turns light brown and the filling is bubbling all over. For an extra crispy finish, broil the cobbler for 1-3 minutes, but keep a close eye on it to prevent burning. Check every 60 seconds!