Step 1: Cook the Pasta Just Short of Done - Bring a large pot of salted water to a boil and cook the ziti until it is about one to two minutes shy of al dente. You want it tender enough to bend but still firm in the center when you take a bite. That little bit of firmness matters because the pasta keeps cooking once it goes into the slow cooker. Drain it well, but do not rinse it. The bit of starch clinging to the noodles helps the sauce hold on to every piece.
Step 2: Prepare the Slow Cooker - Lightly coat the inside of a six quart slow cooker with nonstick cooking spray. This is one of those little steps that saves you from having to scrub baked on cheese later, and I am always thankful for that when dinner is over and the kitchen is quiet. Set the slow cooker aside while you make the sauce.
Step 3: Stir Together the Creamy Sauce - In a large mixing bowl, add the marinara sauce, Alfredo sauce, ricotta, shredded fontina, Italian seasoning, garlic powder, black pepper, half of the Parmesan and Romano cheese, and one half cup of the mozzarella. Stir everything together until the ricotta is mostly blended and the cheese is spread evenly through the sauce. The sauce should look creamy, rosy, and thick enough to cling to a spoon. Do not worry if you see a few small bits of ricotta. Those little creamy pockets are one of the best parts once the pasta cooks.
Step 4: Coat the Ziti in Sauce - Add the drained ziti to the bowl with the sauce. Use a large spoon or spatula to gently fold the pasta through the sauce until every tube is coated. Take your time here and stir from the bottom so the sauce reaches all the pasta instead of sitting in one spot. This is the moment where it starts looking like dinner. The sauce fills the hollow centers of the ziti, the cheese starts to soften against the warm pasta, and you know you are close to having something everybody will be happy to see on the table.
Step 5: Fill the Slow Cooker - Pour the pasta mixture into the prepared slow cooker and spread it into an even layer. You do not need to pack it down. Just make sure the pasta is distributed evenly so it warms at the same pace. Sprinkle the remaining mozzarella over the top. That top layer melts into a soft blanket of cheese while the pasta cooks, and it makes the first scoop especially satisfying.
Step 6: Make the Buttery Crumb Topping - In a small bowl, stir together the remaining Parmesan and Romano cheese, panko breadcrumbs, and melted butter. Mix until the crumbs look lightly coated and the cheese is spread throughout. Sprinkle this mixture evenly over the mozzarella layer. The slow cooker will warm the topping and make it buttery, but it will not become deeply crisp under the lid. That is completely fine for an easy weeknight dinner. For that more traditional al forno finish, you can broil the pasta after it is cooked.
Step 7: Cook Until Hot and Bubbly - Cover the slow cooker and cook on low for two to three hours. Check it around the two hour mark, especially if your slow cooker tends to run hot. You are looking for pasta that is hot throughout, sauce bubbling gently around the edges, and cheese that is fully melted. Try not to cook it much longer than needed. The pasta is already mostly cooked, so extra time can make it softer than you want. Once it is ready, turn off the heat and let it rest with the lid off for five to ten minutes. That short rest gives the sauce time to settle and thicken a little before serving.
Step 8: Broil for a Golden Finish - For a more golden, restaurant style topping, carefully transfer the cooked pasta to an oven safe baking dish. Place it under the broiler for two to three minutes, watching closely the entire time. The topping can go from golden to too dark quickly, so stay nearby. Once the crumbs are lightly browned and the cheese is bubbling, take it out and sprinkle with chopped parsley. Let it sit for a few minutes before scooping. Then bring it to the table while it is still steaming and watch everybody lean in.