Heat the kitchen stove to 180 °C (convection oven 160 °C / gas mark 2-3).
Onion puree: In a frying pan with butter, season the onions with salt and pepper, add the bay leaf and roast gently until soft. Add the sugar, caramelize and season well with salt and freshly ground pepper.
In the meantime, rinse, shake dry and clean the stalk mushrooms, cut the stalks into coarse pieces and lightly shred the leaves.
Season the meat slices with salt and pepper. Mix the two types of mustard well, coat the meat slices thinly on both sides, turn them in flour to the other side (so that the mustard does not burn during frying), fry them in a frying pan with clarified butter on both sides, then cook them in the stove for another ten minutes.
In the meantime, sauté the stemmed walnut stems in a frying pan with the butter, then add the leaves and sauté until soft.
Remove the meat from the stove, coat it again with mustard and add the onion puree. Keep warm in the stove.
Deglaze the pan with clear soup and boil by half. Stir in whipped cream, bring to a boil briefly and season the sauce.
Serve the meat with the sauce and the mush. Serve with boiled potatoes.
Tip: Did you know that one bowl of spinach covers almost the entire requirement of manganese and fiber?