Mix the marinade ingredients and marinate the steak in the refrigerator for 30 minutes to an hour.
Boil the potatoes briefly in salted water until a fork will pierce them easily. Drain.
Drain the steak, reserving the marinade. Slice against the grain into strips ⅓-½" thick.
Heat a cast iron skillet over medium heat until hot. Add the olive oil and 2 T. butter. Add the potatoes to the skillet, arranging in one layer. Cook undisturbed for 3 or 4 minutes. Flip the potatoes and cook undisturbed for another 3 or 4 minutes until nicely browned. Remove from the skillet and set aside.
Add the last 2 T. of butter to the skillet. Add the herbs and garlic and cook one minute, stirring. Working in batches, add the steak strips in a single layer. Cook 1 minute, turn over and cook another minute. Remove to a plate and continue until all of the steak is browned and set aside.
When all the steak strips are browned and you've set them aside, add the reserved marinade to the hot pan. Bring to a boil and boil, stirring, for a minute or so. Add the steak back to the pan and toss with the sauce, then move all of the steak to one side of the pan. Add the potatoes to the other side and stir to coat the potatoes with the sauce. Let the potatoes heat through and serve.