If you heat your cast iron for 10 minutes or so before putting the steak in, cast iron is ideal for pan sauces because it retains heat so well. Cast iron doesn't heat evenly unless it's on the stove top for a while or preheated in the oven at 300ºF or so. But correctly heated, and seasoned, the surface is great for scraping the fond to form a fantastic base for quick butter and wine based sauces like a brown butter, fresh thyme, shallot, Bordeaux reduction. Cast iron is excellent at brown butter sauces because of the heat retention vs Al or SS which can easily burn. With the pan out of the oven, you don't need a flame, just throw in the shallots and butter, deglaze, add the thyme or herb of choice, turn on a flame, add wine and reduce. You get a silky smooth rich sauce; having some demi glace on hand will make it even richer.
