How to Make It
In a large (not nonstick) frying pan over high heat, boil port, cream, and broth until large shiny bubbles form and sauce is reduced to about 1/2 cup, about 15 minutes. As sauce begins to reduce, stir often. Pour into a small bowl and add 1 oz. (2 tbsp.) cheese; stir until cheese is melted. Rinse pan and wipe dry.
Season steak with salt and pepper. Return frying pan to high heat, add oil, and swirl to coat pan. Lay steak in pan and brown on both sides, about 6 minutes total for rare, 8 minutes total for medium-rare; turn pieces occasionally. As fat accumulates, tilt pan to pool fat, then soak up with a wad of paper towels.
When steak is done, transfer to a platter and tent with foil to keep warm. Pour sauce back into pan and stir to scrape up browned bits.
Slice steak across the grain, drizzle with sauce, and top with green onions and remaining 2 oz. cheese, breaking it into small chunks as you go.