Put flour and pepper in a bowl. Make a well in the center. Fill with the melted butter and beaten egg yolks. Work with a wooden spoon, gradually working in the flour.
Beat egg whites until stiff but not dry. Fold into flour mixture. The dough should be light but firm.
Shape into small balls and poach them boiling stock or soup 10 minutes. When they have risen to the top of the liquid they are ready to serve.