Add the olive oil, butter, and onion to a saucepan or Dutch oven over a medium flame. Cook and stir the onion until translucent and aromatic, then add the celery, carrots and garlic with a pinch of Kosher salt. Cook for about 3-4 minutes, stirring the vegetables to coat them well.
Add the lamb meat, a large pinch of Kosher salt and a few grindings of pepper. Crumble the meat with a fork and stir until it is browned.
Add milk or half and half and let it simmer gently, stirring frequently until it has bubbled away. Add nutmeg and bay leaf and stir.
Add the wine and let it simmer until evaporated. Add the tomatoes and freshly grated Locatelli Pecorino Romano, and stir thoroughly. When the tomatoes bubble, lower the heat so the sauce simmers on the lowest possible flame. Cook uncovered, stirring occasionally, until the liquid is reduced until about half, about 1 1/2-2 hours. Scrape any bits up from the bottom of the pan when stirring. While the sauce is cooking, it may begin to dry out and the fat separates from the actual meat so add a little water when necessary, but in the end no water should be left when you serve it. Add salt and pepper to taste. Remove bay leaf when ready to serve.
Bring a large pot of salted water to boil. When the pasta is cooked al dente, remove and set aside a cup of the pasta water. Drain the pasta.
Toss the ragù with the drained pasta, adding an additional tablespoon of butter and 1 tablespoon of extra virgin olive oil and the reserved pasta water, tossing until the butter is melted and fully incorporated, and serve with grated Pecorino Romano, crushed red pepper and fresh torn mint, if desired.