Sauté the Flavor Base: Heat butter and olive oil in a large saucepan over medium heat until sizzling. Add onion, carrot, celery and garlic; cook and stir until onion is translucent, about 5 minutes.
Simmer the Soup: Add tomatoes, water, salt, pepper, crushed red pepper and basil. Stir and bring to boil; reduce heat and simmer 15 minutes.
Blend and Finish: To finish the soup, remove from heat and stir in cream; blend in the pan with an immersion blender or blend in batches in a traditional blender. (Important note: Blending hot liquids in a traditional blender will blow the lid off which will make a mess and could burn you. Instead, use a towel to cover the top of of the pitcher while blending instead of the lid.) Return blended soup to pan and season to taste with salt and pepper; reheat to simmer if needed.
Make the Croutons: Meanwhile make the croutons: Preheat oven to 400˚F. Add bread cubes to a medium bowl and drizzle with olive oil; toss to coat. Spread cubes in a single layer on a baking sheet and season to taste with kosher salt. Bake 15 to 20 minutes until golden and crisp. Remove from oven and set aside.
Serve: Serve bisque hot topped with croutons.
Video
Notes
Texture: For a perfectly smooth bisque, blend until no bits remain and strain through a fine sieve if you like, using a rubber spatula to help press it through. If you prefer a more rustic soup with some texture, just pulse the blender until the vegetables are in tiny pieces but still visible.
Blender Safety: When blending hot liquids in a traditional blender, never seal the lid. Cover the top with a folded kitchen towel to allow steam to escape safely.
Tomatoes: I find that using a high-quality brand of canned whole tomatoes (like San Marzano or fire-roasted) gives the most consistent, deep flavor for this bisque.