For the choux pastry soup, boil 1/16 l water with butter and a pinch of salt. Add the sifted flour and toast, stirring constantly, until the mixture separates from the utensils and spoon.
Remove from heat and allow to cool. Whisk in egg and yolk, season with a pinch of nutmeg and mix everything together to form a soft choux pastry.
If necessary, add a little more egg white. Heat oil in a pan about two fingers high. Cut out small doughnuts from the choux pastry with the help of two coffee spoons and place them in the hot fat.
Bake until golden brown on all sides and drain well on paper towels.
Add the doughnuts to boiling hot beef soup and serve the choux pastry soup sprinkled with chives.