Place the peeled and cubed potatoes into a large pot and cover them with cold water. Add a pinch of salt and bring the water to a boil over medium-high heat. Cook for about 15 to 20 minutes, or until the potatoes are very tender when pierced with a fork. Drain them thoroughly in a colander.
Return the drained potatoes to the warm pot for a minute to allow any excess moisture to evaporate. Use a potato ricer or a fine-mesh food mill to mash the potatoes into a large mixing bowl. This ensures a perfectly smooth texture without any lumps, which is essential for piping through a star tip later.
Stir in the softened butter until it is completely melted and combined. In a small separate bowl, whisk together the heavy cream and egg yolks, then gradually fold them into the potatoes. Add the nutmeg, salt, and pepper, stirring until the mixture is uniform and holds its shape well.
Preheat your oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper. Transfer the potato mixture into a large piping bag fitted with a large star tip. Pipe the potatoes onto the sheet in swirls or rosettes, making them about 2 to 3 inches wide. Brush the tops gently with a little melted butter.
Place the baking sheet in the oven and bake for 15 to 20 minutes. Keep a close eye on them, as you want the edges to become a beautiful golden brown while the centers remain soft. Once they are finished, let them sit for a couple of minutes on the tray to firm up before serving.
