I bring a large pot of salted water to a rolling boil and cook the spaghetti until just al dente. Draining it a minute early works well since it finishes cooking in the sauce later. I always save a cup of the starchy pasta water before draining.

While the pasta cooks, I heat olive oil in a large skillet over medium-high heat and add the ground beef. I break it apart with my spoon and let it brown fully, draining off any excess grease so the sauce doesn't turn oily.

Once the beef is browned, I push it to one side and add the chopped onion and garlic straight into the same pan. I let them soften for about two minutes until fragrant, which builds a nice flavor base for the sauce.

Next, I sprinkle in the Cajun seasoning and smoked paprika, stirring everything together with the beef. I let it cook for another minute so the spices toast slightly and release their full aroma into the meat.

I lower the heat and stir in the butter until melted, then pour in the heavy cream and milk. I let this simmer gently for a few minutes, stirring often so it doesn't scorch on the bottom of the pan.

With the heat still low, I add the cheddar, mozzarella, and Parmesan a handful at a time, stirring constantly. This slow approach keeps the sauce smooth instead of clumpy or greasy.

I add the drained spaghetti directly into the skillet and toss everything together using tongs, adding splashes of reserved pasta water until the sauce clings perfectly to every strand.

Finally, I taste and adjust the seasoning, then top the dish with fresh parsley and an extra pinch of Parmesan before bringing it straight to the table while it's hot and glossy.