Bring a saucepan of salted water to the boil.
Rub oil into the steak, season, and fry in a hot pan with butter for 2-3 minutes per side.
Remove the steak from the pan and let it rest.
Sauté sliced onions in olive oil and butter for 8-10 minutes until golden-brown.
Boil potatoes, carrots, and asparagus for 5-6 minutes then drain.
Return vegetables to the pan with butter and 30ml water and cook for 4-5 minutes.
Reduce red wine by half in a saucepan then stir in beef stock and arrowroot slurry.
Whisk butter into the sauce until melted.
Plate the onions, top with steak, add vegetables, and drizzle with sauce.