Cut head of garlic in half, place on a square of aluminium foil and drizzle with olive oil. Wrap. Bake at 200 degrees C for 45 minutes.
Squeeze roasted garlic cloves out of skins and mash. Set aside.
Sprinkle steak with salt and a generous amount of freshly ground pepper. Heat a large heavy frying pan over medium high heat, but do not add fat.
When hot, cook seasoned steak until seared and well browned on both sides, about a minute per side.
Reduce heat to medium and add 1/2 of the butter. Continue to cook for 3 to 5 minutes on each side. Remove meat, and keep warm.
Pour off the fat in the frying pan, and add the spring onions and red wine. Bring to the boil and whisk in the mashed garlic. Boil until the wine is reduced by half and is thick and syrupy.
As it boils, scrape up browned bits with a wooden spoon. Stir in the meat juices that have accumulated under the steak. Boil for another second or so. Remove from the heat and stir in the remaining butter until it is incorporated into the wine sauce.
Quickly slice the meat against the grain into thin strips. Arrange on a serving plate and pour the sauce down the centre of the slices. Serve immediately.