Preheat oven to 350°F. Grease a 9x13-inch baking pan.
In a large bowl, combine the apples, melted butter, lemon juice, brown sugar, and granulated sugar. Toss well until the apples are evenly coated. Stir in the flour. Transfer to your prepared baking dish.
2½ pounds apples, 4 tablespoons unsalted butter, 2 tablespoons lemon juice, 1 cup brown sugar, ½ cup granulated sugar, ⅓ cup all-purpose flour
In another large bowl, whisk the flour, brown sugar, cinnamon, baking powder, and salt together.
2 cups all-purpose flour, ⅓ cup brown sugar, 2 teaspoons ground cinnamon, 2 teaspoons baking powder, ½ teaspoon kosher salt
Add in the butter and use a pastry cutter or fork to cut the butter into the flour until it is crumbly and the largest pieces of butter are pea sized or smaller.
8 tablespoons unsalted butter
In a liquid measuring cup, whisk together the milk and vanilla extract. Pour the liquid into the dry and stir gently until just combined.
¾ cup whole milk, 1 teaspoon pure vanilla extract
Drop spoonfuls of the topping over the apples. Sprinkle with turbinado sugar.
1-2 tablespoons turbinado sugar
Bake for 40-50 minutes until the apple filling is bubbling and the topping is golden. Cool for 10 minutes before serving.