In a large pot over medium heat, melt some butter and add thinly sliced onions. Cook them slowly, stirring occasionally, until they are caramelized and golden brown, about 15-20 minutes. This step is crucial for developing that rich onion flavor.

Add your choice of beef to the pot with the caramelized onions and cook until the meat is browned. Make sure to break it up into small pieces for even cooking and flavor distribution.

Pour in the beef broth and season the mixture with salt, pepper, and any additional herbs you prefer. Let it simmer for about 10 minutes to allow the flavors to meld together.

Stir in the tortellini and cook according to the package instructions until they are tender. This usually takes about 3-5 minutes for fresh tortellini and slightly longer for frozen.

Once the tortellini is cooked, stir in your choice of cheese until it melts into the dish, creating a creamy and delicious sauce that envelops the pasta and beef.