Ingredients

Step by step

1. Take the steaks out of the fridge about half an hour before you want to cook them.
2. For the pommes mousseline, put the potatoes in a saucepan and cover with cold water. Add a good pinch of fine salt, cover, and bring to the boil. Then turn the heat down and simmer gently – don't boil them – for about 30 minutes, until the potatoes feel soft when gently squeezed.
3. When ready, remove from the heat. One at a time, use a slotted spoon to take the potatoes out of the water and, wearing clean rubber gloves (as they'll be very hot), peel off the skin with a small sharp knife. As soon as they're all peeled, work them through a sieve (or use a food mill or mouli if you have one). Be careful not to scrape or drag the potatoes across the sieve so that they don't turn gluey.
4. Tip the puréed potatoes into a clean pan. Bring the milk and cream to boiling point in another pan, then remove from the heat. Using a rubber spatula, beat one-third of the creamy milk into the potatoes over a medium heat, followed by one-third of the diced butter.
5. Carry on beating in the milk and butter in two more batches. The potatoes will become shiny and silky smooth. Make sure each batch of milk and butter is fully incorporated before adding the next, and switch to a balloon whisk when the purée gets to the liquid stage. The purée should be as smooth as silk after adding all the hot creamy milk and butter, and quite runny. Season to taste and set aside.
6. Preheat the oven to 200°C, fan 180°C, gas 6. Coarsely crush the peppercorns and salt using a pestle and mortar. Brush the steaks on all sides with the Dijon mustard – to give the peppercorns a sticky surface to cling to – then roll them in the crushed peppercorns on a flat surface and pat them firmly with your hands to make sure they stick evenly.
7. Put a large ovenproof frying pan over a high heat. When hot, pour in the oil and heat until it is hot, then fry the steaks for 6 minutes, turning regularly, until they are seared all over. Add the butter and let it melt into the hot oil – it calms everything down and turns the fats and juices a nut-brown colour.
8. Transfer the pan of steaks to the oven and roast for 4 minutes for rare meat or 7 for medium. Baste the steaks with the juices from the pan halfway through cooking.
9. Remove from the oven and rest for 5 minutes. Gently reheat the pommes mousseline. Cut each steak into four even slices and serve with the potato and some green veg. Drizzle with the pan juices.