Peel the rutabagas and cut them into large chunks. Then, cook the rutabagas. You can do this by boiling them in salted water for about 35-40 minutes OR you can cook them in the Instant Pot. To cook them in the Instant Pot, place the rutabaga pieces on the trivet and then pour 2 cups of water into the pot. Cook on HIGH for 10 minutes with a 10 minute natural release.
Preheat the oven to 325 degrees Fahrenheit.
When the rutabagas are cooked, drain them, then mash them with a potato masher.
In a separate bowl, combine the heavy whipping cream, nutmeg, salt, eggs, molasses, cinnamon, ground ginger, and breadcrumbs together. Then, mix that into the mashed rutabagas.
Spray a 8x8 pan with nonstick spray, then pour the rutabaga mixture into the pan.
Sprinkle the breadcrumbs on top. You can use your spoon or a knife to create a design on the top of the casserole.
Slice the butter into 9 equal squares, and place the butter on top of the breadcrumbs so that it will melt during baking.
Bake the casserole for about 1 hour. Cut into squares, serve, and enjoy!