Preheat oven to 400 degrees. Toss together the tomatoes, 1/4 cup olive oil, balsamic vinegar, salt and pepper on a baking sheet. Spread out on the baking sheet and roast in the over for 45 minutes. I will turn the tomatoes after 20-25 minutes.
The original recipe calls for ripe, plum tomatoes. I can't always find them, so use whatever is available.
While the tomatoes are roasting, I continue prepping as follows. In an 8-quart stock pot, over medium heat, add the 2 tablespoons olive oil and the butter. To this, saute the onions, garlic and red pepper flakes for 10 minutes or until the onions start to brown.
To the stock pot add the canned tomatoes, basil, thyme and chicken stock. Turn heat off.
Once the oven roasted tomatoes are done, add the roasted tomatoes and all the liquid on the baking sheet to the stock pot.
Bring the stock pot to a boil and simmer, uncovered for 40 minutes.
Pass mixture through a food mill fitted with the coarsest blade. If you don't have a food mill, you can use your blender. Because the mixture is hot, you will need to put the soup in the blender in small batches.
I usually only blend one-half of the mixture. This will leave you with a more chunky soup. If you want to blend all of the soup, that's OK too.
I have also roasted the tomatoes a day ahead and added them cold to the stock pot. This works well too!
Serve with grated Parmesan Cheese and bread. Yummy!