steak fat and juices - watch the video to see (from cooking steak in a cast iron skillet)
shallots - watch the video to see (finely chopped)
butter - watch the video to see
mushrooms - watch the video to see (chopped)
garlic - watch the video to see (sliced)
cognac - watch the video to see
double cream - watch the video to see
Dijon mustard - watch the video to see
Worcestershire sauce - watch the video to see
beef stock - watch the video to see (reduced)
parsley - watch the video to see (chopped)
salt - to taste (to taste)
pepper - to taste (to taste)
lemon juice or vinegar - as required (as required)