Preheat oven to 400°F. Drizzle a little olive oil over the garlic bulbs and wrap them tightly in a foil pouch. Roast 30-40 minutes until golden and very soft, remove and reduce heat to 350°F.
Arrange tomatoes on two baking sheets and drizzle with olive oil. Season with salt and pepper. Strip 5-6 small stems of thyme for each pan and sprinkle over the tomatoes. Roast 1 hour or until well-slumped.
Char peppers over an open flame on a stovetop or under a broiler until the skins are evenly blackened and papery at the edges. Place in a bowl, cover and cool. Peel and seed peppers.
Working in 2 batches, place a tray of tomatoes, cloves from 1 bulb of roasted garlic squished from skins, 1 roasted red pepper and 2 leaves of fresh basil in high-power blender (like a Vitamix) or a food processor and purée. Repeat with remaining tomatoes, garlic, pepper and basil. Combine in pot and simmer to keep warm.
Bring a large pot of water to a rolling boil, salt water and cook pasta to
al dente. Reserve a little starchy cooking water just before draining pasta, a cup or so.
Toss the pasta with butter, if using, and half of the sauce. Serve pasta in shallow bowls or family-style on a large platter topped with remaining sauce. Pass lots of cheese at table.