In 10-inch skillet, melt butter over medium-high heat. Add onions and garlic; cook 7 minutes. Reduce heat to medium. Add flour; cook 3 minutes, stirring constantly, until browned. Stir in tomato paste and Cajun seasoning; cook 3 minutes, stirring often. In food processor or blender, place onion mixture and remaining 4 cups broth. Cover; process until smooth. Add to vegetable mixture in Dutch oven. Stir in whipping cream and salt. Heat to boiling over medium heat; reduce heat to medium-low. Simmer 15 minutes, stirring often. Garnish individual servings with croutons and parsley.