Peel and cook the potatoes with a pinch of salt. Cut the butter in cubes. Beat the egg. Place baking paper on a baking tray. Preheat the oven at 190 °C.

Drain the cooked potatoes. Mash the potatoes to a fine puree. Mix with a wooden spoon, while adding the egg and butter to the puree until the mixture is smooth. Season with salt, pepper and nutmeg. Put the puree in a piping bag with a serrated mouthpiece and make rosettes (approximately 4 cm in diameter) onto the lined baking tray. Place the baking tray in the middle of the oven and bake the rosettes for 25 minutes, or until golden brown.