2) In a large non-aluminium stockpot, heat the butter and olive oil over medium heat. Add the shallots and cook for 5 minutes, then add the garlic and cook for 3 more minutes or until the shallots are translucent. Add the tomatoes, saffron, parsley, thyme, wine, salt and pepper. Bring to a boil.
3) Add the mussels, stir well, then cover the pot and cook over a medium heat for 8 to 10 minutes, until all the mussels are opened (discard any that do not open). With the lid on, shake the pot once or twice to be sure the mussels don't burn on the bottom. Pour mussels and sauce into a large bowl and serve hot.