1. Preheat the oven to180°C, gas mark 4, and a deep-fat fryer to 180°C.
2. Place the potatoes and some salt in a pan of cold water and bring to the boil. Boil for 10 minutes then drain in a colander and set aside until needed.
3. Coat the shallots in the corn our and deep fry until they are a light golden colour. Remove from the fryer using a slotted spoon and drain onto clean kitchen paper. Season with a little salt then add to a bowl with the breadcrumbs and chives and
4. Preheat a frying pan. Rub the beef with 1 tbsp of the vegetable oil and season well. Place in the pan and colour evenly on all sides. Transfer to the oven for 5 minutes for rare, then remove and leave to rest.
5. Mix the mustard and red wine vinegar together then spread all over the beef llet and roll in the breadcrumb mixture. Reserve some of the crumbs for garnish. Once thoroughly coated, leave to one side.
6. Meanwhile, heat a heavy-based pan, add 1 tbsp of the vegetable oil and cook the onion and mushrooms on a high heat for
2 minutes then add the pancetta. Once evenly coloured, remove from the pan onto clean kitchen paper. Place the pan back on the heat and add another 1 tbsp vegetable oil and half of the butter. Once melted, add the parboiled potatoes. Cook for 5 minutes, then add the rest of the butter and continue to cook until the potatoes are a rich golden brown. Drain off any excess oil then return the mushrooms, onions and pancetta to the pan and cook for a further 2 minutes. Remove from the heat, sprinkle with the parsley and keep warm.
7. Prepare the salad cream by placing all the ingredients except the cream into a blender and blitz for 1 minute. Slowly drizzle in the cream until the mixture begins to thicken and is velvety and smooth. Taste for salt and white pepper and set aside.
8. Drizzle the little gem halves with the remaining 1 tbsp vegetable oil and season with salt and pepper. Place cut-side down onto a preheated chargrill pan and cook for 2-3 minutes until charred. Remove and set aside.
9. On a large serving platter, place the little gem halves in a row along the centre, cut-side up. Cut the beef into 0.5cm slices and layer on top of the lettuce. Drizzle liberally with the anchovy salad cream and scatter over the remaining breadcrumbs. Serve with the forestier potatoes.