In your slow cooker add tomatoes, wine, broth, tomato paste, onions, celery, carrots, fennel bulb, garlic, crushed red pepper flakes, sugar, salt and pepper and stir to combine.
I always use 2 cans of diced tomatoes. Sometimes one 28 oz and one 14 oz or two 28 oz cans because we are bread scoopers and dippers. We also love this sauce.
Cook on low for at least 2 hours or on high for 1 hour. Vegetables must be tender.
When you are ready to prepare your mussels you first you have to clean and scrub them. Next, you must remove their beards. You do this by pulling out the hair-like strands around the shell of each mussel, usually with a knife. If you see any shells that are open, discard them. Discard any that are cracked or not sealed shut.
Add mussels, cover and cook on high until the mussels open, between 15 and 25 minutes. Discard any mussels that do not open. Add cream, stir and serve.
Any mussels that do not open while cooking may be dead and as the flesh deteriorates, the bacteria that is created can cause severe food poisoning amongst other things. You must discard all of the mussels that did not open up.