Steamed Mussels: Simmer all ingred except mussels for 2 minutes. Add mussels, cover pot and steam over high heat until mussels open, about 4 minutes. (Discard mussels that do not open.) Remove mussels from shells, Strain liquid in pot through double thickness of wet cheesecloth and reserve for risotto.
Risotto: Saute onion in butter over med-low heat in heavy suacepan until lightly colored but not browned, about 2 minutes.
Meanwhile, combine strained mussel stock and enough chicken stock to make 5c and heat to bare simmer. In seperate small pan, boil saffron in 1/2c of the stock to dissolve. Set aside.
Raise heat under onion to medium, add wine and allow to evaporate. Add rice and cook 3-4 minutes, stirring to coat thoroughly.
A half cup at a time at first and less later, add simmering stock to rice, stirring constantly. When rice has nearly absorbed each portion of stock, add another. After 14-15 minutes, add saffron with its hot stock. Rice should be cooked to desired firmness in 18-20 minutes, and 4-5c of the stock will be needed. Remove from heat and salt and pepper to taste. Stir in mussels. Sprinkle with parsley and serve.