Preheat your oven to 350°F and grease a medium-sized baking dish.
In a large skillet over medium heat, add butter and sauté the onions until soft.
Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Season with salt and pepper, then stir in the tomato soup and milk until well combined.
Fold in the cooked noodles and give everything a gentle toss to coat evenly.
Pour the mixture into the prepared baking dish and sprinkle with shredded cheddar cheese.
Bake uncovered for about 25 minutes, or until the cheese is bubbly and slightly golden.
Let it rest for a few minutes before serving — trust me, it’s worth the wait.