Wash the savoy cabbage leaves, dab dry and cut into fine strips. Peel and halve the onion and cut into strips. Peel and wash carrots, slice lengthwise and then cut into fine strips.
Clean the leek, cut it into 3 cm long pieces, halve them and also cut them into strips. Heat the oil in a pot. Sauté the vegetables briefly, add 500 ml water and bring to the boil.
Stir in 2/3 of the onion soup powder. Cook soup for 10-12 minutes. Stir in miso paste, let it stand for a few minutes and serve.