Sirloin in mustard cream

1/4 cup unsalted butter
1 1/2 pound sirloin steak or 4 boneless fillets
Salt and pepper
1 tablespoon Dijon mustard
1/4 cup dry Vermouth
1/2 cup whipping cream
1 tablespoon minced chives

Heat a large frying pan, add 1 tablespoon of the butter, and when it stops foaming add the meat. Saute on both sides until browned and cooked to desired state. Season with salt and pepper. Remove to a platter and keep warm. Mix together the mustard, Vermouth, and cream and stir into the pan juices. Boil, scraping up the drippings. Add the remaining butter to the pan and heat, stirring until blended. Remove from heat. Slice the whole steak on the diagonal, or leave the fillets whole, spoon over the sauce, and sprinkle with chives.