Peel and wash the potatoes. Cook in boiling salted water for about 20 minutes until soft. Drain and steam the potatoes. Press them through a potato press while still hot. Stir in 4 egg yolks and 4 tbsp. milk.
Season with salt and 2 pinches of nutmeg.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Grease a muffin baking tray (12 troughs). Pour the potato mixture into a piping bag with a large star-shaped spout and squirt into the wells.
Whisk 1 egg yolk and 2 tablespoons of milk. Spread the tuffs with it. Bake in a hot oven for 15-20 minutes. For an e.g. Mediterranean flavour, add melted butter with some garlic and basil.