Wash and peel the potatoes, cut them into 1-1/2-inch chunks, and place in a large saucepan. Cover with 1 1/2 to 2 inches of cold water over the potatoes and put salt generously.
2
Bring the potatoes to a boil over high heat. Reduce the heat to medium low and simmer until the potatoes can be easily pierced with a knife, about 15min. Drain in a colander.
3
Return the potatoes to the pot and mash with a potato masher until get very smooth. While the potatoes are still warm, mix in the egg yolks 1 at a time, making sure each yolk is completely incorporated before adding the next.
4
Add the butter, cream, measured salt, pepper, and nutmeg and stir until the butter melts and the mixture is smooth.
5
Transfer in to a large piping bag fitted with a 1cm piping tip and pipe 12 round mounds (2 1/2 inches wide by 4 inches tall) onto each prepared baking sheet. Place baking sheets in the preheated oven at 200C and bake until the tops of the potatoes are light golden brown, about 25min.