1/ About half an hr before you are going to cook take the steak out of the fridge to come up to room temp. 10 mins before you're going to cook them drizzle with the olive oil and salt and pepper.
2/ Put a large, high sided frying pan (skillet) on a high heat and when it's really hot add the steaks. Cook the steaks to your liking. I go about 3 mins a side depending on how thick they are. Go just under where you would normally cook them to because they're going to get a tiny bit more cooking at the end. Remove the steak and set aside to rest.
3/ Turn the heat down to medium and put the diced onions and garlic in the pan with the knob of butter. Cook them for 5 mins until they start to soften.
4/ Add the spices and cook for a min or so. Then turn up the heat again and add the brandy. Cook off for a min or so.
5/ Add the stock, bring up to the boil and simmer for a few mins until it's reduce by a third to a half.
6/ Slice the steak (against the grain) into strips 1 cm wide and then add that plus any juices back to the pan along with the sour cream, parsely and spinach and black pepper. Stir together and remove off the heat after a min.