Preheat broiler. Place peppers on a foil-lined baking sheet, skin side up. Broil 4 in. from heat until skins are blistered, about 5 minutes. Transfer to a bowl; let stand, covered, 20 minutes. Change oven setting to bake; preheat oven to 400°., Toss cauliflower with 2 tablespoons oil; spread in a 15x10x1-in. pan. Roast until tender, 25-30 minutes, stirring occasionally. Remove skin and seeds from peppers; chop peppers., In a 6-qt. stockpot, heat remaining 2 Tbsp. oil over medium heat. Add onion; cook until golden and softened, 6-8 minutes, stirring occasionally. Add garlic, rosemary and paprika; cook and stir 1 minute. Stir in flour until blended; cook and stir 1 minute. Gradually stir in stock. Bring to a boil, stirring constantly; cook and stir until thickened., Stir in cauliflower and peppers. Puree soup using an immersion blender. Or, cool slightly and puree soup in batches in a blender; return to pot. Stir in milk and remaining seasonings; heat through. If desired, serve with Parmesan. , Freeze option: Freeze cooled soup in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally; add a little stock or milk if necessary.