Place onions and butter into the Thermomix bowl and chop 3 sec/speed 6. Sauté 5 min/Varoma/speed 1.
Add sweet potato and potato, stock and pepper and cook 30 min/90ºC/speed 2.
Add fish, prawns, scallops and cream and allow heat of the soup to cook the seafood for a few minutes.
Stir gently before serving with snipped fresh parsley and dill.