For the beef roulades in mustard sauce, wash and clean the leek and cut into fine rings.
Spread the beef cutlets, season with salt and pepper and spread with mustard. Put a sheet of ham on each one and spread the leek on top.
Roll up the roulades tightly and fix them with roladeneedles.
Heat the olive oil in a large frying pan and brown the roulades in batches on all sides.
Pour in the beef broth and simmer, covered, for about 1 hour.
Remove the roulades from the pan and keep warm.
Mix the crème fraîche with the remaining mustard and stir into the gravy. Finish with the vermouth.
Place the beef roulades once again in the mustard sauce and serve.