Heat a large skillet over medium-high heat and add the ground beef, breaking it apart with a spoon as it cooks. Once the beef is mostly browned (about 5-7 minutes), add the diced onion and cook for another 2-3 minutes until softened. Stir in the garlic and cook for 30 seconds until fragrant. I like to let the meat develop a nice golden color before draining—this creates deeper, richer flavors in the final casserole. Drain excess fat from the pan using a colander or by tilting the pan and spooning it out.

While the meat cooks, bring a large pot of salted water to a boil and add the pasta. Cook according to package directions until just al dente (usually 8-10 minutes)—it should still have a slight firmness since it will continue cooking in the oven. Drain well and set aside. I prefer rotini because its ridged shape and spiral hold the creamy sauce beautifully, unlike smaller pasta shapes that can get lost.

To the cooked ground beef in the skillet, add the mushroom soup, milk, Worcestershire sauce, salt, pepper, and thyme. Stir well to combine, then add the sliced mushrooms. Simmer over medium-low heat for 3-4 minutes, stirring occasionally, until the mushrooms are just tender and the sauce is smooth and cohesive. This gentle heating allows all the flavors to meld without overcooking the mushrooms.

Preheat the oven to 350°F. In a 9x13 inch baking dish, spread half of the meat sauce from Step 3 as the base layer. Top with half of the cooked pasta from Step 2, then sprinkle with half of the grated cheddar cheese (about 4 oz). Add the remaining meat sauce, then the remaining pasta, creating a final layer. Reserve the remaining 4 oz of cheese for the top. This layering technique ensures even distribution of sauce and flavors throughout the casserole.

Bake the casserole uncovered at 350°F for 15-18 minutes until the edges are bubbly and the dish is heated through. Remove from the oven and sprinkle the reserved 4 oz of cheddar cheese evenly over the top. Return to the oven for another 4-5 minutes until the cheese is melted and slightly golden. I always use Tillamook cheddar because it has a superior melting quality that creates a creamy, cohesive top layer rather than a greasy one.

Remove the casserole from the oven and let it rest for 3-4 minutes before serving—this allows the sauce to set slightly so portions hold together neatly when scooped. Sprinkle the fresh chopped parsley over the top just before serving for a pop of color and fresh brightness against the rich, creamy casserole.