Peel and wash the potatoes and cut them roughly into pieces. Cover and cook in boiling salted water for about 20 minutes. Meanwhile peel onion and garlic and chop finely. Heat the fat in a pan.
Fry the onion and garlic until transparent. Add undefrosted spinach and heat over low heat, stirring several times for about 10 minutes. Bring to the boil briefly. Season with salt, pepper and nutmeg.
Drain the potatoes and press them through a potato ricer. Mix potatoes and spinach and season with salt, pepper and nutmeg again. Form the puree into dumplings and arrange on plates.