Preheat oven to 375° and spray a 13 x 9 baking dish with a non stick spray.
Peel and slice apples 1/4" thick and place in a large mixing bowl.
Sprinkle sugar, brown sugar, lemon juice, corn starch, cinnamon and nutmeg over apples. Stir and let sit for 5 minutes., stir again and pour apples into prepared baking dish. Set aside.
In a medium mixing bowl, whisk flour, sugar, brown sugar, baking powder and salt together. Add butter, and with a fork or pasty blender, mix until crumbly.
Pour boiling water to flour mixture and stir until combined.
Spoon mixture over apples and spread gently making sure all the apples are covered.
Sprinkle with a little extra sugar and cinnamon on top and pop in the oven.
Bake uncovered for 55-60 minutes or until topping is baked thoroughly and has started to brown.
Serve warm topped wth vanilla ice cream.