Preheat oven to 375° and spray a 13 x 9 or a 3 quart baking dish with a non stick spray right before adding the berry mixture.
Pour berries into a large bowl and rinse.
Sprinkle berries with sugar, lemon juice, and corn starch. Stir and let sit for 10 minutes. Stir one more time.
Pour berries into prepared baking dish.
In a medium mixing bowl, whisk flour, sugar, brown sugar, baking powder and salt together.
Using a pastry blender, or a fork, mix butter into flour mixture until crumbly.
Pour boiling water into flour mixture and stir until combined.
Spoon mixture over berries and spread gently making sure berries are covered completely.
Sprinkle additional sugar on top of batter.
Bake uncovered for 55-60 minutes or until topping is cooked thoroughly and has started to brown.
Serve warm topped with vanilla ice cream.