Blend ketchup and lemon juice (if apples are very tart, add 1 - 2 Tbsp. Sugar to ketchup mixture). Combine sugar, flour and cinnamon; cut in butter until thoroughly mixed. Fill pie shell with apples; top with sugar mixture. Bake in 375 degree oven 40 - 45 minutes or until apples are cooked. Serve warm with vanilla ice cream if desired.