Add water and cornstarch in a bowl and mix to combine. Place cornstarch mixture, sugar and all berries in a large skillet over medium high heat. Stir mixture and heat until it starts boil. Pour mixture into a 9×13 pan and set aside to cool completely.
Add remaining dry ingredients and whisk to combine. Add applesauce to mixture. Add in butter and use a pastry blender or two forks and cut butter into mixture. Sprinkle mixture over cooled berry mixture. Bake at 400 degrees F for about 30-35 minutes or until filling is thick and bubbly and topping is golden brown. Remove from oven; let cool for 20 minutes. Top with ice cream. Devour.
Recipe by pretty plain janes at https://prettyplainjanes.com/2013/05/15/mixed-berry-crumble/