Preheat the oven to 350 degrees F. Butter a 2-quart casserole dish and set aside.
Add the potatoes to a large pot of cold, salted water. Bring to a boil over high heat, then reduce the heat and simmer until the potatoes are tender, about 20 minutes. Drain in a colander in the sink.
Mash the potatoes in a large bowl. Add the evaporated milk, brown sugar, butter, vanilla, cinnamon, beaten eggs, salt and pepper, to taste. Mix together until smooth. Pour the mixture into the casserole dish and bake for 25 minutes.
In a small bowl, toss together the cashews, marshmallows, and coconut. Remove the casserole dish from oven and top with the cashew mixture. Bake until the marshmallows are lightly toasted, about 5 to 10 more minutes. Remove the casserole from the oven and let cool for 5 minutes before serving.