Whisk together the cinnamon sugar and set aside.
Preheat oven to 350° F. Grease a 9x13 baking dish (or similar size).
Add the apples, brown sugar, flour, lemon juice, cinnamon, nutmeg, allspice and salt to a pot. Cook on medium heat stirring until the apples are coated and start to soften, 4-5 minutes.
Remove the saucepan from the heat and stir in the vanilla. Transfer the apples to the prepared baking dish.
In a mixing bowl whisk together the flour, baking powder, sugar, cinnamon, and salt. Pour in the melted butter and milk and whisk until combined.
Pour the batter on top of the apples. Use a rubber spatula to spread it into an even layer so that all of the apples are covered.
Sprinkle the cinnamon sugar on top of the batter and then place the baking dish onto the center rack of the oven. Bake for 35-40 minutes or until a toothpick inserted into the topping comes out clean.
Remove from the oven onto a cooling rack and let it cool for 5 minutes before serving. Serve warm on it's own or with vanilla ice cream, whipped cream, or caramel sauce.