A properly cooked fillet steak is a joy to enjoy. Cooking a fillet (tenderloin) is not difficult either. Simply sear it on either side and throw the pan into a hot oven for a few minutes and the job is practically done. You can complicate the process and clog your arteries by finishing it (and yourself too) with butter. I have never seen the need to do this. A good fillet is a good fillet. Right?