Blanche tomatoes in boiling water & shock in ice water. Peel, rough chop, and set aside.
Melt garlic butter in large Dutch oven over medium-low heat. Add chopped onion, cover and sweat onions until tender.
Add flour and stir to coat onions. (Will be very thickly coated.) Reduce heat to low and cook a minute or two to remove the raw flour taste.
Gradually add half & half and water, stirring until well blended, allowing to thicken for a few minutes.
Add the chopped tomatoes, tomato puree and tomato paste. Cook at a low simmer for about 30 minutes.
Process with an immersion blender in the Dutch oven. When smooth, add chopped basil and stir to combine.
Serve with Parmesan cheese and garnish with additional fresh basil