Preheat the oven to 220°C (approximately 430°F).
Peel potatoes and boil in salted water for about 25 minutes until done. Drain and evaporate over low heat.
Press potatoes through a ricer. Mix potatoes, butter and egg yolks. Season with salt, pepper and nutmeg.
Put mixture into a pastry bag with a large star tip and pipe rosetees onto a greased baking sheet. Brush with melted butter and bake until golden brown for about 10 minutes. Remove and serve with sprigs of thyme.
