Place potatoes in a large pot and cover with a few inches of cold water. Add salt to the water and bring to a simmer. Cook until the potatoes are tender- about 20-25 minutes.
While the potatoes are boiling, melt 2 tablespoons of butter and set aside- to be used to coat the potatoes right before going into the oven.
Preheat the oven to 425°.
When the potatoes are cooked, drain, and place back in the pot set over low heat. Allow them to release steam for a minute or so. Add 2 tablespoons of butter and mash the potatoes until the butter has been incorporated.
Add in nutmeg, black pepper, heavy cream and continue mashing the potatoes. Once everything is incorporated, add salt to taste and the egg yolks. Continue to mash until the mixture is smooth. Avoid over mashing.
Using a piping bag with a large star point, pipe the potatoes onto a cookie sheet. Alternatively, fill a casserole dish with the mashed potatoes, and use a fork to create lots of peaks on the surface.
Whether you make piped portions or a casserole, glaze the potatoes with the melted butter.
Bake in the 425°F oven until nicely browned, about 20 minutes.