Preheat oven to 400F.

Toss together the halved tomatoes, 1/4 cup olive oil, salt, and pepper in a large bowl.

Spread the tomato mixture in a single layer on a baking sheet.

Roast the tomatoes for 45 minutes, or until softened and slightly caramelized.

In a 8 quart stockpot over medium heat, saute the chopped onions and minced garlic with 2 tablespoons of olive oil, the butter, and red pepper flakes for 10 minutes, until the onions begin to brown and soften.

Add the canned tomatoes (with juice), fresh basil leaves, and fresh thyme leaves to the stockpot.

Add the roasted tomatoes, including any liquid from the baking sheet, to the stockpot.

Bring the mixture to a boil, then reduce heat and simmer uncovered for 40 minutes, allowing the flavors to meld.

Pass the soup through a food mill fitted with the coarsest blade to remove skins and seeds, creating a smooth texture.

Taste the soup and adjust seasoning as needed with additional salt and pepper.

Serve the roasted tomato basil soup hot or cold, garnished with fresh basil if desired.