Peel the potatoes and cut into 1 inch cubes. Place in a saucepan and add water to cover the potatoes. Place on the stovetop over high heat. Bring to a boil, then reduce to a simmer. Let cook for 15–20 minutes, or until the potatoes are easily pierced with a fork.
Preheat oven to 400°F.
Drain the potatoes and place them in the bowl of a stand mixer. Add the butter. Mix on low until potatoes are mashed and creamy (be careful not to overmix or they will get glue-like).
Add the egg yolks, cream, salt, pepper, and nutmeg. Mix until just combined. Let sit for 30 minutes to cool.
Prepare a large sheet pan with parchment paper or a silicone mat.
Once the potatoes are cool, place them in a piping bag fitted with a star tip. Pipe the potatoes into 3 inch circles, swirling the piping bag to create a mound of potatoes.
Brush the tops of the potatoes with the egg wash. Bake for 20–25 minutes, or until golden brown on top. Serve immediately.