Clean mushrooms, perhaps rinse, cut into slices. Peel onion, cut into cubes. Rub cutlets dry. Fry in hot clarified butter for 2-3 minutes on each side. Season with salt and pepper. Remove and keep warm.
Roast mushrooms and onion in the frying fat for approx. 5 min. Season with salt and pepper. Dust with flour, sweat briefly. Add stock and whipping cream while stirring, bring to a boil and simmer gently for about 5 minutes. Season to taste with salt and freshly ground pepper.
In the meantime, cook sparrows in boiling salted water for 2-3 minutes.
Drain. In the saucepan melt butter. Toss the sparrows in it.
Serve cutlets with sauce and sparrows. Sprinkle with fried onions. Serve with green salad with lemon dressing.
By the way: Did you know that clarified butter is obtained by extracting water, milk protein and lactose from butter?