Peel onion and chop finely. Peel and roughly grate the carrots and potatoes. Pat the rasp dry well with kitchen paper. Then mix well with onion, flour and egg yolk and season well with salt, pepper and nutmeg.
Heat the oil in a coated pan. Pour the mixture into the pan as small rösti in portions and fry on each side for 3-4 minutes over medium heat until crispy and brown. Serve hot.