Make the soffrito. Finely chopped onion, carrot, and celery. Yes, you can do this in a food processor. No, we don't generally. We like the soffrito to have some texture, not turn into pulp.
Sweat the veggies. Heat olive oil and butter in a large dutch oven over medium-low to medium heat. Add the onion and cook for 3 minutes until translucent. Raise the heat to medium, then add the carrot and celery. Cook for an additional 5 minutes, stirring occasionally.
Brown the meat. Increase the heat to medium-high, then add the ground beef and ground pork. Season the meat immediately with 2 tsp Kosher salt and ½ tsp black pepper. Let this cook about 8-10 minutes, stirring often and breaking up the meat with a wooden spoon or spatula.
Deglaze the pan. Pour in red wine, allowing it to reduce and evaporate, about 3-4 minutes. Don't worry, all the flavor stays behind!
Skim the fat. Once the wine reduces, you'll see excess fat float to the top of the pan. Use a spoon to skim the fat, then discard. This will yield about ¾ - 1 cup of fat. Removing this makes the bolognese sauce less greasy.
Add remaining liquid. Pour in the whole milk and chicken stock. Next, crush the tomatoes with your hands directly into the pot. Add two bay leaves and -- the most important part of the recipe! -- ½ lb finely chopped chicken livers.
Simmer low and slow. Allow the sauce to simmer over low heat for 3 hours, checking on it and stirring every 30 minutes or so. If the heat is at a proper simmer, you shouldn't need to add any additional liquid at all.
Finish the sauce. Remove the bay leaves, then add freshly chopped rosemary and thyme. Taste and adjust seasoning, as needed.
When ready to serve, cook pasta. Cook rigatoni or other pasta according to package directions for al dente, meaning just slightly undercooked by 1-2 minutes. This is important! Before draining, reserve 1 cup pasta cooking water. Drain pasta, do NOT rinse, and set aside.
Cook with pasta in the sauce. Transfer as much bolognese as you want to a large skillet. Heat over medium high heat until bubbly. Add al dente rigatoni or other pasta shape directly to the pan. Cook, stirring or shaking the pan often, so that each piece of pasta is completely coated with sauce. The final step: add a couple tablespoons (more, if making a lot of pasta) of the reserved pasta cooking water to help bind the sauce together. The starch from cooking the pasta will thicken the sauce and bring it to life!
To serve. Add a couple tablespoons (more, if making a lot of pasta) of the reserved pasta cooking water to help bind the sauce together. Divide pasta between bowls, then serve with grated lemon zest and freshly grated Parmesan!