For the pepper sauce, first crush the peppercorns in a mortar and steam them in the foaming butter in a saucepan until soft. Finally, add the diced onion and sauté until soft.
Pour in port wine or Madeira and simmer. Fill up with the clear soup and let it simmer again, finally add the whipped cream and let it bubble gently to the desired consistency.
Season the sauce with salt and blend finely. If you don’t like to bite on peppercorns, strain the pepper sauce through a sieve.