Preheat the oven to about 180C. Fill a metal roasting tin with the oil and preheat.
Take the steaks out of the fridge and let them come to room temperature.
Slice the potatoes into quite thin sticks, skin on. Wash them in a bowl of cold water and then drain, leaving on a teatowel to dry as much as possible.
Add the chips to the hot oil and throw in the rosemary, tossing them to cover well in herbs and oil. Let them roast for about 40 minutes, turning them a few times.
When the chips are nearly done, heat a heavy bottomed frying pan so that it is smoking hot and you can't hold your hand over it.
Whilst the pan is heating up, lightly oil the steaks and cover with as much ground pepper as you'd like. I like a lot!
Add the steaks to the pan (don't overcrowd the pan, if doubling up and doing 4 then do it in two batches - if you overcrowd the pan they will steam). Let them fry for 2 minutes on each side for rare (just how I like it!), 3 minutes on each side for medium, and 4 for well done. Turn the steaks over and when the time is up take out and rest on a warm plate. Season with a little salt whilst resting.
Keeping the pan on a high heat, add the brandy and deglaze, scraping the bits from the bottom of the pan with a wooden spoon, add the stock and let this liquid reduce by about half. Whisk in the butter and taste. It shouldn't need any salt if using commercial stock. You may want to add a little more pepper or even some cream. Add the juices of the resting steak to the sauce and turn down the heat until ready to serve. Dress the salad at the last minute.