Wash and cut tomatoes in half (if you use anything smaller than a Campari tomato, leave it whole). Place them on a large baling sheet with the onion, garlic and thyme. Drizzle olive oil over the veggies and sprinkle with Kosher salt and a few generous turns of freshly ground pepper. Give everything a toss. Roast in the oven for 25 to 30 minutes until the veggies are carmelized.
Remove the thyme sprigs and pour the mixture into a medium sized stock pot or Dutch oven. Be sure to get all the juices. Add chicken broth and the bay leaf. Bring to a boil. Simmer for 25 to 30 minutes. Let cool slightly and then puree by either an immersion blender or puree in a regular blender (for a smoother texture). You can also strain the mixture if you want a more elegant soup.
Check for seasonings. Serve immediately or refrigerate (no longer than 2-3 days) and reheat later.
Garnish with a dollop of creme fraiche or other toppings, as desired.