Cook the pasta according to the package instructions. Drain well.
Heat a non-stick pan or skillet over medium heat. Add the butter and beef, brown the beef while breaking it up into smaller pieces.
Stir in the flour and cook for about 2 minutes.
Gradually whisk in the milk until smooth. Bring to a simmer while stirring occasionally. Once the sauce starts to thicken, add in the cheese and whisk until smooth with no lumps. The sauce should be thick and creamy.
Stir in the pasta. Season with salt and pepper to taste before serving. Garnish with parsley.