Step 1In a food processor, process the salt, garlic, basil and cheese until well combined. Slowly add in the oil, and process only until mixed. Set aside. Makes about one-half cup.
Step 1Heat the oven to 400 degrees. Place the tomatoes, cut side up, in a large roasting pan. Add the salt, thyme, pepper, garlic and onion, shaking the pan so that the ingredients settle around the tomatoes. Roast for 2 hours. After 1 hour and 15 minutes, pour off some of the liquid and reserve, leaving enough liquid to cover the bottom of the pan. Remove the tomatoes from the oven and allow to cool slightly.
Step 2Remove the thyme sprigs. Blend the tomatoes with both the reserved liquid and the liquid remaining in the pan in a blender in batches (or with an immersion blender). Pour the soup through a strainer, pressing firmly on the solids. Chill overnight. The next day, serve cool or at room temperature, with the optional pistou, a dollop of cr?me fra?che or torn basil leaves.