01 - Bring a large pot of salted water to a boil. Cook the cheese tortellini according to package directions until tender. Drain thoroughly and set aside.
02 - Pat the sirloin pieces dry and season generously with salt and freshly ground black pepper on all sides.
03 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add the steak pieces in a single layer, working in batches if needed. Sear for 2 to 3 minutes per side until a deep golden-brown crust forms and the steak reaches your preferred doneness. Transfer to a plate and tent loosely with foil.
04 - Reduce the heat to medium. Add the butter to the same skillet and let it melt. Sauté the shallots and minced garlic, stirring constantly, until fragrant and softened, about 1 minute.
05 - Pour in the heavy cream, scraping up any browned bits from the bottom of the pan. Bring to a gentle simmer and cook for 2 to 3 minutes, allowing the sauce to reduce and thicken slightly.
06 - Stir in the grated Parmesan cheese, continuing to stir until fully melted and the sauce is smooth and velvety.
07 - Return the cooked tortellini and seared steak to the skillet. Toss gently to coat everything evenly in the garlic cream sauce and heat through, 1 to 2 minutes.
08 - Transfer to warm plates or a serving dish. Sprinkle generously with chopped fresh parsley and serve immediately.