Heat oil in a large saucepan over medium-high heat. Add onion; sauté 4 minutes or until tender. Add 6 cups tomato; cook 2 minutes. Reduce heat to low; stir in broth and garlic. Simmer, covered, 30 minutes.
Uncover; simmer 45 minutes or until reduced to about 6 cups. Drain broth mixture through a sieve into a large bowl; discard solids. Return broth to pan. Stir in 7 cups tomatoes, salt, and pepper; bring to a boil. Reduce heat; simmer, uncovered, 10 minutes.
Remove soup from heat. Stir in basil, rind, and butter.