Heat oven to 375°. Grease bottom and sides of square baking dish, 8x8x2 inches, with shortening. Mix granulated sugar and cornstarch in 3-quart saucepan. Add berries and lemon juice; toss until evenly coated. Heat to boiling over medium-low heat. Boil 3 to 4 minutes, stirring frequently, until thickened. Spoon berry mixture into baking dish.