Preheat oven to 400°F.
In a large pot boil the peeled potatoes. Once they are fork tender drain the water off and put them back in the pot to cook over low heat for 3 minutes (this will help dry them out).
Mash the potatoes until they are smooth. To do this you can use a potato masher, hand mixer, or a potato ricer.
Let the potatoes cool for 5 minutes then add the butter, salt, pepper, nutmeg, and cream.
Mix thoroughly and add more salt if needed.
Fold egg yolks into the mixture until they are combined. Do not over mix.
Add potato mixture to a large piping bag with a large star tip and pipe the potatoes onto parchment paper or a silpat mat, on a baking sheet.
Place the baking sheet in the freezer for 30 minutes. This will firm up the potatoes to help with the next step.
Mix whole egg with milk and gently brush egg wash over potatoes. Be careful not to use too much egg wash, you do not want it to drip down the sides and pool around the potatoes. (if you are making these ahead of time wait to add the egg wash until you are ready to place them in the oven.)
Bake for 20 - 25 minutes, or until edges of potatoes are golden brown.