1. Preheat oven to 400°.
2. Place a 9-inch cast-iron skillet in preheated oven; heat 5 minutes. Remove pan from oven, and lightly coat with cooking spray.
3. Combine cornstarch, juice, dash of salt, and cherries in a large bowl, tossing well to coat. Pour cherry mixture into prepared pan.
4. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 4 ingredients (through 1/8 teaspoon salt) in a medium bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Sprinkle flour mixture over cherries. Place skillet on a jelly-roll pan. Bake at 400° for 35 minutes or until filling is thick and bubbly and topping is browned. Remove from oven; let stand 20 minutes. Serve warm.