16 extra-large white mushrooms
5 tablespoons good olive oil, divided
2 1/2 tablespoons Marsala wine or medium sherry
3/4 pound sweet Italian sausage, removed from the casings
6 scallions, white and green parts, minced
2 garlic cloves minced
2/3 cup panko crumbs
5 ounces mascarpone cheese, preferably from Italy
1/3 cup freshly grated Parmesan
2 1/2 tablespoons minced fresh parsley leaves
Salt and freshly ground black pepper