Roasting vegetables gives this bisque a deeper, richer flavor.
Preheat two ovens to 450°F. If you only have one oven, arrange the racks so that they're evenly spaced to accommodate a good air flow.
Lightly grease one sheet pan with extra virgin olive oil and assemble the cut tomatoes onto the pan in a single layer.
Roast the tomatoes for 30-35 minutes, or until they are browned on the edges.
Toss the celery, carrots, and onions in 2 tablespoons of olive oil.
Nestle the head of garlic (cut side up) in a square piece of heavy-duty aluminum foil and pour the remaining olive oil over it. Tightly wrap up the garlic in the foil and place the garlic onto the pan with the veggies.
Roast the veggies for 30-35 minutes as well. When roasted they should look brown and nicely caramelized.
Once the vegetables are finished roasting, transfer everything except the garlic to a dutch oven.
Pour a 1/2 cup of the chicken stock onto the sheet pans and use a wooden spoon to scrape up the browned bits from the pans. Add this liquid to the dutch oven along with the tomatoes, the veggies, and the bay leaf.
Add the sugar, salt, pepper, and the rest of the chicken stock to the pot. Bring the mixture up to a boil, and reduce the heat to low and simmer, covered, for 15 minutes.
Once the soup has finished cooking, use an immersion blender to puree the mixture*. After a few pulses with the immersion blender, take the head of garlic, and squeeze half of it into the pot, then continue blending until smooth.
Remove the pot from the heat and stir in the chopped basil and the cream.
Stir the cream in well. If you're using very cold cream, you may have to return the pot to the stove and heat it until warmed through. Be sure to avoid boiling the bisque once the cream has been added.
Preheat your broiler (use a low broil setting if you have one).
Arrange the slices of Italian bread on a small sheet pan and toast the slices until they're slightly crisp- about 1 1/2 minutes per side.
Remove the pan from the oven and smear the remaining roasted garlic onto each slice of bread. Place a slice of the gruyere cheese on top of each bread slice and return the pan to the oven to broil.
Broil just until the cheese begins to melt and remove the pan from the oven.
Spoon the Roasted Tomato-Basil Bisque in individual bowls and top each serving with a cheesy crouton. Serve while hot.
*If you don't have an immersion blender, you'll need to carefully transfer the soup to your blender and puree it in batches. Remember to vent the lid to prevent an explosion