Cut the pretzels into thin slices. Heat the butter with 1 tablespoon of oil in the pan. Fry the pretzels in it until golden brown, then drain on kitchen paper.
Cut the onions into thin slices. Wash the parsley and shake dry, pluck the leaves off.
Soak the veal sausages in boiling water for 10 - 12 minutes, but do not let them boil. Peel and cut into slices while still warm.
Whisk the mustard with the remaining oil, vinegar and 2 - 3 tablespoons of water and season with salt and pepper. Mix everything together and serve.