Have your butcher trim all the fat off the rumpsteak. Cut into thin slices then into ribbons. Heat 2 tablespoons of butter in a frying pan. As soon as it becomes clear, put in half of the minced beef. Quickly brown all over, keeping the meat rare inside. Take out and fry the second half in the same way. It is necessary to brown the meat in two steps to keep it rare inside. Put the remaining butter into the frying pan and fry the finely chopped shallots gently over a very moderate heat. Stir, add 4 tablespoons of cream to deglaze the pan, scraping the bottom with the back of a fork. Reduce over a high heat while stirring, add the remaining cream and the mustard. Salt, pepper. Boil. Add the meat and the juice it gave out. Reheat up to the boiling point, serve straight away. If the cream is too liquid when you want to add the meat, dissolve 1 teaspoon of cornstarch into a little cold water, remove the sauce from the heat and mix it in.
