Season steak with salt and pepper. Press the seasoning into the meat to create an even coating.
Heat the vegetable oil and 1 tablespoon of butter in a large skillet over medium-high heat until just smoking. Add the steak to the pan and sear for 4 minutes. Turn and sear the other side for another 4 minutes for medium-rare. Once cooked to desired doneness, transfer the steak to a cutting board to rest.
Reduce the heat to medium and add the brandy or cognac to the skillet. Allow the alcohol to cook down for about 1 minute while stirring to scrape off any browned bits in the bottom of the pan. Once the alcohol has reduced by half, add the cream, Dijon mustard, and remaining tablespoon of butter and continue to cook until mixture begins to reduce and thicken, 5-7 minutes.
If desired, slice steaks against the grain and serve topped with the finished sauce.