1. Heat reserved skillet, without washing, over high heat. Once hot, remove skillet from heat, and carefully pour in vermouth; using a wooden spoon, scrape up any browned bits. Cook until wine is almost completely reduced, about 45 seconds.

2. Stir in mustard, about 15 seconds. Add cream and any juices that have collected under steak; stir to combine. Pour over steak, and serve immediately.