Step 1: Brown the Ground Beef - Set a large skillet over medium heat and add the ground beef. Break it into small crumbles with a wooden spoon or sturdy spatula as it cooks, making sure no large pieces stay hidden and pink in the middle. I like to keep the crumbles fairly small because they spread through the pasta better and give you a little beef in every forkful. Cook until the meat is fully browned and no pink remains.
Step 2: Season the Beef - Sprinkle the salt, black pepper, garlic powder, and onion powder evenly over the browned beef. Stir well so the seasonings coat the meat instead of sitting in one corner of the skillet. Seasoning at this stage matters because the warm beef absorbs those flavors, giving the finished sauce a savory foundation rather than relying on cheese alone.
Step 3: Soften the Onion and Garlic - Add the diced onion to the skillet and cook for 3 to 4 minutes, stirring now and then, until it looks softened and slightly translucent. Stir in the minced garlic and cook for about 30 seconds, just until you can smell it. Garlic can turn bitter if it cooks too long, so this quick finish is all it needs. Drain any excess grease before moving on.
Step 4: Build the Slow Cooker Sauce - Transfer the beef, onion, and garlic mixture to a 6 quart slow cooker. Add the undrained Rotel, beef broth, cheddar cheese soup, cubed Velveeta, and cubed cream cheese. Stir gently to spread everything around. The mixture will not look smooth yet, and that is completely fine. The slow heat will soften the cheeses and bring the sauce together.
Step 5: Let the Cheese Melt Slowly - Cover the slow cooker and cook on LOW for 3 to 4 hours or on HIGH for about 2 hours. Stir once or twice if you are nearby, scraping around the edges and folding the soft cheese into the liquid. When the cooking time is up, stir until the Velveeta and cream cheese have completely melted and the sauce looks smooth, creamy, and evenly colored.
Step 6: Cook the Cavatappi - Near the end of the slow cooker time, bring a large pot of salted water to a boil. Add the cavatappi and cook it according to the package directions until al dente. You want the pasta tender but still holding its shape, since it will spend a few more minutes in the warm sauce. Drain it well, but do not rinse it, because the starch on the pasta helps the cheese sauce cling.
Step 7: Finish with Cheddar and Pasta - Add the drained cavatappi to the slow cooker, followed by the freshly shredded sharp cheddar. Stir slowly but thoroughly until the cheddar melts and every curl of pasta is coated. At first it may look like there is more sauce than you need, but the pasta will absorb some as it rests. If the mixture seems unusually thick, add a small splash of beef broth and stir again.
Step 8: Rest and Serve - Cover the slow cooker and let the pasta cook for another 10 to 15 minutes. This short rest helps the noodles take on the flavor of the sauce while the whole dish settles into a creamy, scoopable consistency. Give it one final stir, taste for salt and pepper, then sprinkle chopped green onions over the top. Serve it hot while the cheese is loose and glossy.