Rinse the meat, pat dry and cut into cubes of just under 2 cm.
Heat the oil in a frying pan until it smokes. Fry the meat cubes for 1 1/2 min on all sides, turning continuously over a high heat, without letting any frying juices escape. Form the meat on the spot on kitchen paper to soak up the fat.
Finely grind the meat cubes with the beef broth in an electric mixer, shape into a hair sieve and strain into a saucepan with the back of a wide spoon.
Stir two thirds of the whipped cream and the sherry into the puree.
Heat the soup moderately, stirring throughout, as the gravy could curdle if the heat is too high.
Mix the egg yolk-whipped cream mixture into the soup, heat it for another 2 min on the turned off stove top, but do not let it get too hot.
Remove the soup from the stove and season with salt and pepper. Serve in small heated soup bowls and sprinkle with chervil leaves.