Roast the walnuts in a pan without fat, take them out. Dab the fillet dry well and season with salt and pepper. Heat the oil in the pan. Brown the meat thoroughly all around. Fry over medium heat for 12-15 minutes, turning.
Mix mayonnaise and sour cream. Season to taste with lemon juice, salt, chilli and a little sugar. Remove the fillet, wrap it in aluminium foil and let it rest for about 10 minutes.
Clean, wash and finely dice the celery. Chop the nuts. Peel and core the apple and also dice it finely. Mix everything with the mayonnaise.
Wash the salad, shake dry and arrange on plates. Cut the fillet into thin slices and arrange on top. Spread Waldorf cream over it. Baguette tastes good with it.