Heat your oven to 200°C/Fan 180°C/Gas 6. Fill a pan with water. Add a pinch of salt. Cover and bring to the boil. Peel the potatoes. Slice them into chips about 1 cm thick. Add to the boiling water.
Bring the water back to the boil. Simmer for 3 mins. Drain. Tip the chips into a large roasting tin or baking tray. Drizzle over ½ tbsp oil and mix. Bake for 25-30 mins till golden, turning once or twice.
Rub the tomatoes with 1 tsp oil and season. Pop them on a baking tray or in a small roasting tin. After the chips have been cooking for 15 mins, bung the tomatoes in the oven to roast for 15 mins.
Slice the mushrooms. Peel and crush the garlic. Pick the leaves off half the rosemary sprigs. Finely chop the leaves.
Pick off the large watercress stalks. Pop the watercress in a bowl. Drizzle with 1 tsp oil and season with salt and pepper.
Drizzle 1 tsp over the steaks and season. Heat a griddle or frying pan till it’s smoking hot. Fry for 1-2 mins on each side if you like it rare, 2-3 mins on each side for medium and 4-5 mins on each side for well done.
Pop the steaks on a board or plate and wrap them in foil. Leave them to rest. Add the mushrooms to the pan with a splash of water if needed. Season. Stir in the garlic and rosemary.
Fry the mushrooms over a high heat for 5 mins till golden. Turn the heat down. Add the cream. Stir and cook for 2 mins till the sauce is warm. Taste and adjust the seasoning. Serve the steaks with the chips, watercress, roast tomatoes and mushroom sauce.