Pre heat the oven to 200°C. / 400°F.Season the turkey breast portions with salt and pepper.
Heat a roasting tin on the hob over moderate heat, add 2 tbsp. oil and 15g butter and when the butter is foaming, add the turkey breasts and cook until browned on both sides. Transfer the tin to the oven and cook for 20 minutes or until the turkey is done.
Meanwhile, cook the vegetables.
Pan fry the mushrooms over a high heat in 2 tbsp oil and 15g butter. In another pan, fry the sliced potatoes with 2 tbsp.oil and 15g butter until golden brown. Cook the leeks in another pan with 15g butter, a good splash of water and a little salt and pepper for about 3 minutes or until the water has evaporated, and the leeks are tender. Keep all the vegetables warm.
Remove the turkey from the oven and allow to rest for 5 minutes in a warm place. To make the sauce, tip off excess fat from the turkey pan, add the shallots to the pan over a gentle heat and cook for 2 minutes. Stir in the wine, scraping the bottom of the pan to loosen all the caramelised juices. Boil until almost all the wine has evaporated, then add the water and bring to the boil again. Add the rosemary, and then whisk in the remaining 15g butter.
To serve, spoon the vegetables attractively around the outside of the plate. Slice the turkey breasts, and fan the slices in the centre. Top with a little sauce and serve.