Peel the 4 whole cloves of garlic and set them in a small pan. Cover them with milk and cook slowly over medium heat for 9 minutes. Drain the excess milk through a strainer and place the garlic in a food processor, mixing until smooth. (Reserve the garlic puree in a small container; it will keep in the refrigerator for several days.)
In a hot sauté pan, sear the lamb with a drizzle of olive oil. Sear the lamb until it has a nice brown crust. Remove the meat from the pan and season to taste with salt and pepper. Reserve.
For the potato mash, place the peeled fingerling potatoes in a large saucepan over medium-high heat with enough water to cover the potatoes and add a pinch of sea salt. Cook the potatoes until they are tender and then pass them through a good mill. Season to taste with olive oil, some of the garlic puree, salt, pepper and a touch of fresh nutmeg. Add the finely chopped chives at the end.
Set aside about 1 teaspoon of the chopped rosemary and place the rest on a plate. Cover the lamb in garlic puree and then roll it in the chopped rosemary to coat.
Place the lamb in a baking dish and finish cooking it under the broiler to get a light crust from the rosemary and garlic (about 4-5 minutes). Reserve the drippings. Allow the lamb to rest in a warm place.
In a saucepan over medium heat, add the lamb drippings, white wine, the clove of chopped garlic, tomato and reserved 1 teaspoon rosemary leaves; reduce for 20 minutes or until you achieve a sauce-like consistency. Add the unsalted butter to finish the sauce.
In a sauté pan with a drizzle of olive oil, sauté the baby spinach with freshly ground pepper.
On a plate, arrange the spinach and mash in a ring. Add the lamb and drizzle the sauce over it.