Melt the butter in a large pot over medium heat. Add the onions and garlic and cook, stirring occasionally, until the onions are tender and translucent, about 10 minutes.
Add the canned tomatoes and carefully break them apart with your hands or a masher until they are in small chunks. Drain the jar of roasted red peppers and add them to the pot, along with the stock.
Turn heat to high, bring to a simmer, then reduce heat and simmer, partially covered for 20 minutes.
While soup is cooking heat olive oil in a skillet. Add the bread cubes and saute, stirring often, until the bread is gloriously toasty and golden brown. Season croutons with salt and pepper and set aside.
After the 20 minutes of cooking time, puree soup using an immersion blender, or a regular one. If you use a regular blender, take care to vent the soup to allow steam to escape.
Taste soup for seasoning, and add salt and pepper to taste. Stir in the heavy cream, top with croutons and an additional drizzle of heavy cream, if desired. Serve immediately.