Step 1Cook the onions and minced garlic in the olive oil in a large roasting pan over medium heat (using 2 burners, if necessary) until the onions turn transparent, 4 to 5 minutes.
Step 2Make 12 slits evenly over the surface of the roast and insert a sliver of garlic into each.
Step 3Add the roast and garlic sausages to the pan, then the tomatoes, breaking them up with your hands as they go in the pan. Add the carrots, basil, salt and pepper. Bring to boil.
Step 1Place the bread, eggs, parsley, garlic, Parmesan, pine nuts, salt, pepper and ground beef in a large mixing bowl. Gently combine until ingredients are blended. Shape the mixture into 24 (2-inch) meatballs.
Step 2Add the meatballs to the sauce and reduce the heat to a simmer. Cover the roasting pan tightly with foil and cook 15 minutes longer. Adjust the foil so that the pan is loosely covered and continue to simmer over very low heat until the meat is fork tender but not dry, 3 1/2 to 4 hours.
Step 1Cook the pasta in boiling salted water until al dente; drain.
Step 2Remove the meat from the sauce using a slotted spoon and tongs. Skim any excess fat from the sauce. While the pasta is cooking you may want to reduce the sauce to thicken it, 10 to 15 minutes.
Step 3Carve the roast and assemble the slices on a serving platter with the sausages and meatballs. Mix a portion of the sauce, about 3 or 4 cups, with the mostaccioli and serve the remaining sauce on the side.