Step 1: Cook the Beef and Onion
Start by browning the ground beef in a large skillet over medium heat. Add the chopped onions and minced garlic, letting the onions soften and release their sweetness. Cook until the beef is browned and the onions are translucent, about 6-8 minutes. Drain any excess fat to avoid a greasy casserole.

Step 2: Prepare the Macaroni
While the beef is cooking, bring a large pot of salted water to a boil. Cook the macaroni according to the package instructions until al dente, typically around 7-9 minutes. Drain and set aside.

Step 3: Combine the Ingredients
Once the beef mixture is ready, stir in the cream of mushroom soup, milk, salt, pepper, thyme, and canned mushrooms. This creamy mixture will coat all the ingredients in a savory sauce that’s essential for this comforting casserole.

Step 4: Layer the Casserole
Preheat your oven to 350°F. In a 2-quart casserole dish, start by spreading half of the beef mixture on the bottom. Follow with a layer of cooked macaroni, and then sprinkle a generous handful of sharp cheddar cheese. Repeat this layering process, but save some cheese for the top.

Step 5: Bake
Place the casserole in the oven, uncovered, and bake for 20 minutes. This allows all the flavors to meld together and the cheese to melt beautifully. After 20 minutes, sprinkle the remaining cheese on top and return to the oven for an additional 5-7 minutes, or until the cheese is bubbly and golden brown.

Step 6: Serve and Enjoy!
Once baked, let the casserole sit for a few minutes to set before serving. This dish is best enjoyed warm, with that deliciously gooey cheese pull and a medley of rich flavors in every bite.