In a large skillet, melt butter and olive oil over medium heat. Add sliced onion and cook, stirring occasionally, until softened and lightly caramelized, about 8-10 minutes.
Add minced garlic and cook for another minute until fragrant.
Add ground beef to the skillet. Break it up with a spoon and cook until browned. Drain off any excess grease.
Pour in the beef broth and bring to a simmer. Stir in the heavy cream and dried thyme. Season with salt and pepper to taste.
Add the refrigerated tortellini to the skillet. Stir to combine with the beef and onion mixture. Cover and cook for 5-7 minutes, or until the tortellini are tender and heated through.
Stir in the Gruyere and Parmesan cheeses until melted and creamy.
Serve immediately, garnished with extra cheese if desired.
Notes
This dish is best served fresh. You can add a splash of Worcestershire sauce for extra depth of flavor.