Preheat oven to 350°F and grease a 9x13-inch baking dish.
In a large bowl, toss sliced apples with 1/2 cup sugar, 1 teaspoon cinnamon, nutmeg, and 2 tablespoons flour. Spread evenly in the prepared baking dish.
In another bowl, whisk together 1 1/2 cups flour, 1/2 cup sugar, brown sugar, baking powder, cream of tartar, and salt.
Pour melted butter and buttermilk into the dry ingredients and stir until just combined. Drop large spoonfuls of batter over the apples, spreading slightly but leaving some gaps.
Sprinkle the cinnamon-sugar mixture generously over the top of the batter.
Bake for 42-47 minutes until the topping is golden brown and the apples are tender when pierced with a knife. Cool for 10 minutes before serving.