To prepare croutons: Preheat oven to 350 degrees. Using a serrated knife, cut off and discard bread crusts, and cut bread into 3/4 - to 1-inch cubes.
In a small pan over medium heat, melt 3 tablespoons butter and cook, stirring often, until butter is golden brown and aromatic, about 3 minutes after butter melts. Remove from heat.
Place bread cubes in a medium bowl and pour butter over them, tossing to coat. Season to taste with salt and pepper and toss again. Spread bread cubes on a baking sheet and bake until croutons are toasted and golden, about 20 minutes, stirring occasionally. Remove pan from oven.
To prepare soup: In a large pot or Dutch oven over medium heat, melt 1 tablespoon butter and olive oil. Add onion and garlic and sauté until onion is translucent, about 5 minutes. Add tomatoes, water, cream, salt, pepper, red pepper flakes, celery seed, oregano and sugar. Increase heat to high and bring to a boil, then lower heat to a simmer and simmer for 15 minutes.