Preheat the oven to 220°C.
Peel and dice the potatoes then rinse under clean water. Place in a saucepan and cover with cold, salted water. Bring to the boil and simmer until tender. Drain the potatoes and then crush with the butter. Add a little milk and mix with a spoon to make a fine purée.
Cut the shallots in half.
Place the shallots (cut side down) on a sheet of foil and drizzle with 50ml olive oil and 50ml water. Season with salt and pepper then fold up the foil to make an airtight parcel (keep plenty of air inside the parcel). Place in a hot frying pan and cook for 15 to 20 minutes over a medium heat. Check that all the liquid has evaporated and the shallots are cooked.
Season the steaks with salt.
Heat a frying pan to very hot and add a dash of oil. Sear the steaks on both sides, add the cognac to the pan and reduce to a syrup. Transfer the steaks to the oven and finish cooking for 2-3 minutes depending on the thickness of the steaks.
Use stainless steel serving rings to plate the puréed potatoes. Serve the steak alongside the potatoes and finish with the confit shallots. Garnish with reduced balsamic vinegar to serve.
«You can also thinly slice the shallots and saute in a hot pan until caramelised and soft.»