1 pound pork tenderloin, cut into 8 crosswise pieces
1 tablespoon butter
1 cup fresh mushrooms, sliced
2 tablespoons onion, finely chopped
1-3 teaspoons fresh rosemary, chopped OR 1 teaspoon dried rosemary leaves, crushed
1/4 teaspoon celery salt
1 clove garlic, minced
1 tablespoon sherry
fresh rosemary sprigs, optional
fresh mushrooms, optional