Heat the butter and olive oil in a large, nonreactive pot over low heat; add the mushrooms, garlic, and shallots; and cook for 3 to 4 minutes, or until soft, stirring occasionally. Add the wine, clam juice, and clams. Cover and simmer for 8 to 9 minutes, or until the clams have opened. Discard any clams that do not open.
Divide the linguine, if using, and clams among the serving bowls.
Add salt and pepper, to taste, to the broth. Ladle the broth over the clams, garnish with parsley, and serve.
Variation for broth with body:
After cooking and removing the clams, return the broth to the heat and bring it to a simmer.
In a small bowl, combine 4 teaspoons of all-purpose flour and
4 teaspoons of soft butter.
Add the flour–butter mixture to the broth and cook, whisking constantly, for 2 to 3 minutes, or until the sauce thickens slightly. Ladle, as directed, over the clams.