In a large pot, combine the wine with the bay leaves and bring to a boil. Add the mussels, cover and cook over high heat, shaking the pan a few times, until the mussels open, about 5 minutes. Drain the mussels in a colander set over a medium bowl. Pour the mussel broth into a glass measure. Crumble the saffron into the mussel broth.
Discard any unopened mussels. Remove the mussels from their shells and place in a bowl. Pour the melted butter over the mussels and toss to coat. Cover with plastic wrap.
Heat the extra-virgin olive oil in a large, deep skillet. Add the thinly sliced garlic and cook over low heat just until golden brown, about 4 minutes. Add the crushed red pepper and cook for 1 minute longer. Slowly pour in the reserved mussel broth, stopping when you reach the grit at the bottom of the glass measure. Add the lemon juice and simmer over moderately high heat until the sauce is reduced to about 1 cup, about 8 minutes.
In a large pot of boiling, salted water, cook the spaghetti just until al dente. Drain the pasta well.
Add the buttered mussels and the hot spaghetti to the mussel sauce and toss over low heat until the pasta is uniformly coated. Season with salt and pepper. Transfer to warmed shallow bowls and serve at once.
Make Ahead: The recipe can be prepared through Step 3 and refrigerated separately overnight.
Wine Recommendation: A buttery yet lighter style of Chardonnay will echo the creamy texture of the sauce and stand up to the briny mussels in this pasta. Try the inexpensive 1999 Domaine de Borie Mâcon-Villages Vieilles Vignes or the 1999 Louis Jadot Pouilly-Fuissé.