My mother's mother was a big rutabga fan and I learned to love this homely vegetable from eating them with her. She was a wonderful cook and such an awesome grandma. She served her rutabagas diced and boiled with butter and I think that's my favorite way to eat them. This recipe has a couple extra steps but is really good and the cheese makes it more popular with non-rutabaga lovers.
For this amount of casserole I used about 4 good sized rutabagas, about 1 cup of milk, 4 tbl. butter, 3/4 cup grated parmesan, salt, pepper, and a bit of swiss cheese on top.
Peel and dice rutabagas. Boil in salted water until tender. Drain. Mash rutabagas with milk, butter, parmesan, salt and pepper, just like if you were making mashed potatoes. Put the mixture in a casserole dish and top with cheese. Bake at 350F until the cheese is melted.