It’s not essential to roast your own turkey; lovely carved-by-hand fresh turkey is available in most supermarkets. Roast chicken or slices of ham work equally well.
Preheat the oven to 200°C/400°F/gas 6. Season the turkey with salt and pepper. Heat a roasting tray with some oil and fry the turkey on all sides to a light golden brown. Remove from the heat and transfer the turkey into the centre of a large sheet of foil, spooning over any oil left in the pan and topping with the butter. Seal the foil before returning the turkey to the tray and baking for 55-60 minutes.
Once cooked, remove the turkey from the tray and leave to rest for 20-30 minutes until just warm.
Bring a large saucepan of water to the boil, adding 2teaspoons salt. Plunge the Little Gems into the boiling water and cook for 30-60 seconds until only just beginning to soften. Spoon the lettuces into a colander and leave to drain.
Put the mushrooms into a frying pan with the vinegar and simmer until softened. Stir in the crème fraîche and chives and, once warm, add the lettuce halves, turning them to coat with the mushroom dressing. Season with salt and pepper.
Open the foil bag and remove the turkey, saving any buttery juices. Carve the breast into two to three slices per portion and drizzle with the juices. Divide the salad among the plates, spoon over the cream dressing and top with the turkey slices.