Preheat oven to 300f and move racks to make enough room to accommodate a large Dutch oven pot in the middle of the oven.

Heat a large Dutch oven to medium heat. After the pot is hot add the olive oil. Season the lamb pieces with salt and pepper on all sides then add to the pot. Sear the lamb in batches to avoid overcrowding. Place the seared lamb on a plate and set aside.

Turn the heat down to medium-low. Add the onions, carrots, and celery to the pot and saute until the veggies are very soft (about 12-15 minutes).

Next, add in the tomato paste and cook for 3 minutes stirring frequently. Add the wine and beef stock and turn heat to medium. Using a wooden spoon scrape all the brown bits off the bottom of the pan.

After cooking the wine for 3 minutes, add the plum tomatoes and rosemary and bring to a simmer. Once simmering add the lamb pieces to the pot, stir, then turn off and cover. Cook the ragu in the oven until tender (about 3 hours).

Bring a large pot of salted water (2 tablespoons kosher salt) and cook the rigatoni until very al dente. While the pasta is boiling taste test the ragu and make final adjustments to salt and pepper.

Heat a large pan to medium-low heat and add in 2 cups of the lamb ragu. Add the pasta to the pan and cook for 1-2 more minutes until al dente mixing well to thoroughly coat the pasta.

If the pasta is too dry add more of the ragu but try to not over-sauce. If the pasta seems a little dry add a bit of reserved pasta water to loosen it up. Serve plated with grated Parmigiano Reggiano and the remaining ragu on the side. Enjoy!