To make a yam marshmallow casserole, boil yams for 5 to 10 minutes, drain the water, and mash the potatoes with milk, butter, nutmeg, salt and pepper before spreading into a casserole dish. Top with marshmallows, and bake 15 to 20 minutes at 375 degrees Fahrenheit.
Wash and peel the yams before preparing the dish. Cut the yams into 1-inch pieces so that they cook quickly. Cook about 3 pounds of yams for a 2-quart casserole dish. Cover the yams with about 1 inch of water. Check the yams after boiling for 5 minutes to see if they are soft enough.
The milk and butter added to the mashed yams adds creaminess. Start with 1/2 cup milk and 4 tablespoons butter. Add more if desired, based on your taste and texture preferences. Add milk slowly to keep the yams from getting runny.
Spread the yam mixture evenly into the casserole dish. You can make the casserole up to this point a day in advance. Refrigerate the yams until you are ready to bake them. Spread 2 cups of miniature marshmallows evenly on top of the yams.
The casserole just needs enough time in the oven to heat up the middle and lightly brown the marshmallows. Watch the casserole closely once the marshmallows start to brown, to keep them from burning.