Preheat oven to 350°. In a Dutch oven, saute the celery, red peppers and onions in butter and oil until tender. Add garlic; cook 1 minute longer. Stir in flour until blended; gradually add cream and milk. Bring to a boil; cook and stir 2 minutes or until thickened. Stir in shredded cheese until melted.
Add spinach, artichokes, salt, cayenne, pepper and pepper flakes. Transfer to a 13x9-in. baking dish coated with cooking spray. Sprinkle with Parmesan cheese.