Bring a large pot of salted water to a boil and cook the cheese tortellini according to package directions. Drain and set aside.
Pat the sirloin steak dry and season with salt, black pepper, and garlic powder.
Heat olive oil or butter in a large skillet over medium-high heat. Add the steak in a single layer and sear until browned on all sides. Remove and set aside.
Reduce heat to medium and add butter to the skillet. Stir in the garlic and cook just until fragrant.
Pour in the heavy cream and whole milk, stirring to scrape up any browned bits. Simmer gently until slightly thickened.
Lower the heat and whisk in the Parmesan cheese until smooth. Stir in Italian seasoning and fresh parsley.
Add the cooked tortellini and seared steak back into the skillet. Toss gently until everything is coated in the sauce.
Taste and adjust seasoning with salt and black pepper. Serve warm with extra cracked black pepper on top.