Pour in the cans of diced tomatoes (don't drain), tomato soup, and tomato paste. Add in the onion, garlic, sugar, basil, bay leaf, Italian seasoning, and chicken or vegetable broth (3 for a thicker soup, 4 for thinner).
(I used a Blendtec and did it in 2 batches) Blend or pulse until completely smooth. Pour back into the slow cooker. (Alternatively you can use an immersion blender.)
Season with salt and pepper and stir in the heavy cream.
Cook for 10 minutes or until the raviolis are cooked through. I prefer this soup really thick and each bite filled with ravioli, but you may like a thinner soup with less ravioli so add the ravioli slowly to your desired preference and add additional chicken or vegetable broth if desired.
Cook time varies on the temperature you use (low or high).