01 -
Select 1 pound of meatballs labeled fully cooked. Heat them with the 48 ounces marinara in a covered saucepan using the package stovetop directions, including any required thawing; verify at least 165°F in several centers. Meanwhile, boil the 8 ounces rigatoni in a separate pot according to its package until just tender. Reserve up to 2 cups hot pasta water, then drain. Preheat the slow cooker according to its manual while the stovetop components finish.
02 -
Transfer the hot meatballs, sauce, and drained pasta into the preheated cooker. Fold together, adding reserved hot water only a little at a time if needed to loosen the sauce; do not automatically add all 2 cups. Sprinkle with 1 cup mozzarella, cover, and allow approximately 5–10 minutes for the cheese to melt. Serve promptly, maintaining at least 140°F if holding. Refrigerate shallow leftover portions within 2 hours after hot holding ends, or within 1 hour above 90°F.