Cook the peeled potatoes until tender. Cut the cutlets into strips. Peel and finely dice the onions, fry the meat in portions in hot oil in a large frying pan, remove from the pan. Add a quarter of a liter of water and sprinkle in the sauce powder, simmer for 1 minute. Season with a little pepper, whipped cream, salt and lemon zest. Fold in the meat. Peel potatoes, cut into halves or quarters, toss in hot butter. Sprinkle with minced parsley, season with salt, season with pepper. Halve the plums, remove the seeds, cut into wedges and fold into the ragout, heat briefly together. Serve with parsley potatoes.