Heat oil in a saute pan or grill pan over high heat. Add steaks and sear until deeply browned on both sides. Remove and set aside.
Add onion and garlic to pan and cook until onion is deeply golden. Add beef stock and mustard and whisk to combine. Cook for a couple of minutes to allow the sauce to thicken a bit.
Return steaks to pan and return to “hot but off”
Recipe by Between Carpools at https://betweencarpools.com/how-to-serve-a-perfectly-cooked-steak-on-shabbos/