1️⃣ Bring a pot of generously salted water to a boil for the pasta and preheat the oven to 400F.
2️⃣ In a pan preheated over medium heat, sauté the onion in oil until translucent (2-3 mins) and then add the beef, salt, and pepper; sauté 3-4 more mins until the beef is cooked through and set aside.
3️⃣ In a separate large pot preheated over medium heat, melt the butter and then add the flour; cook the flour whisking constantly for 1 minute and then start gradually pouring in the milk ~1/2 cup at a time, whisking so that the milk gets fully incorporated before adding more.
3️⃣ Once all of the milk is added, turn the heat up to medium high and continue whisking until the white sauce starts to bubble and has thickened slightly, then add the salt, pepper, nutmeg, and cayenne.
4️⃣ Add the chopped cauliflower to the white sauce and cook stirring often (so the white sauce doesn’t burn) for 7-10 minutes until the cauliflower is tender (boil the pasta while the cauliflower is cooking); stir in the cheddar cheese and then turn off the heat until the pasta is ready.
5️⃣ Cook pasta 2 mins less than package directions then drain and transfer it into the cheese sauce; add the beef + onion mixture, tomato, and parsley and cook over medium heat for 1-2 mins.
6️⃣ Transfer the mac into a 9x13” baking dish (or individual bakers) and top with cheese; bake uncovered for 20-25 mins until golden brown and bubbly and enjoy!
