Preheat oven to 325°F.
Place apples in a 13x9” baking dish. Sprinkle with lemon juice and toss to coat.
In a medium bowl, mix together 2 cups sugar, flour, baking powder, 1 teaspoon salt and the cinnamon. Add milk and melted butter, and mix well. Pour batter evenly over apples and set aside.
In a small bowl, mix remaining 1/2 cup sugar, cornstarch and 1 teaspoon salt. Sprinkle over batter. Evenly pour the boiling water on top then transfer to the oven and bake for 50 minutes, until golden brown and bubbling.
Can be served warm or at room temperature, topped with a scoop of pumpkin ice cream and drizzled with caramel sauce.