I will sear the LB in the cast iron skillet, then finish in the oven. Thin sliced, against the grain. Served with horseradish/sour cream sauce, mashed pots and steamed broccoli.
Worcestershire sauce - half a cup or so - with minced garlic, black pepper, oregano, and whatever else strikes me. Put into a Ziploc bag up 24 hours ahead. Easy and tasty.
Oh, and I grill - try to leave it strongly pinkish/red in the middle, then rest for 10 min, covered.
I have yet to need a marinade on an LB. However, I do have some recommendations about prep and cooking. About an hour before cooking time, salt the slab(s) liberally with kosher salt. Bag in a gallon ziplock bag or similar, make sure it’s tight. Put in a sink of warm water and leave it there until the meat and water reach equilibrium, around 70 degrees. Then broil or grill as hot as you oven or grill can go. Be sure to allow the slabs to rest before carving.
The salting replaces nearly everything a basic marinade does, and bringing the slap to room temperature before cooking ensures a faster through-cook without the overcooked gray band.
Credit due to Cook’s/ATK. Most thick beef will cook much better if it’s not put in the oven with a fridge-temp center. Bring it all up to some consistent temp around 60-70 and you will be much more even and predictable cooking.