2 cups uncooked medium pasta shells
1/2 cup butter, divided
1 cup French bread baguette crumbs
1 pound bay scallops
1 cup sliced fresh mushrooms
1 small onion, chopped
3 tablespoons all-purpose flour
3/4 teaspoon dried thyme
1/4 teaspoon salt
1/8 teaspoon pepper
2 cups whole milk
1/2 cup white wine or chicken broth
2 tablespoons sherry or chicken broth
1 cup (4 ounces) shredded Swiss cheese
1 cup (4 ounces) shredded sharp cheddar cheese