Start by heating a big soup pot over medium heat, add the butter and oil and then the chopped onion & garlic.
When the onions are soft, add the chicken stock, tomatoes, sugar, a little red wine vinegar, thyme and salt & pepper.
Raise the heat to medium-high and bring the soup to a simmer. Once at a simmer, lower the heat to low, cover the pot and cook for 45 minutes.
When the soup is done, remove the thyme twigs and puree the soup. You can use a blender or food processor. I like using my hand blender. It works great, is easy to clean and I don't have to lug the big pot over to the food processor and inevitably spill some soup on the counter. I added the heavy cream and roasted peppers just before I pureed the soup but I guess you could add them 5 minutes before the soup is done. For me the peppers were a last minute addition that I wasn't planning from the start and it worked out great.
After pureeing the soup, let it cool down before serving. Taste and adjust seasonings with salt and pepper and serve.