Bring a large pot of well-salted water to a rolling boil. Add the cheese tortellini and cook according to package directions (usually 3-5 minutes for fresh, 7-8 for frozen). Drain thoroughly and set aside without rinsing.

While the tortellini cooks, pat the steak pieces completely dry with paper towels. In a small bowl, combine the salt, black pepper, garlic powder, and smoked paprika. Toss the steak pieces in this mixture until evenly coated.

Heat the olive oil in a large skillet over medium-high heat until shimmering. Add the steak pieces in a single layer without crowding. Sear undisturbed for 2 minutes until a brown crust forms, then flip and cook another 1-2 minutes for medium-rare. Transfer to a plate and let rest for 3-5 minutes.

Reduce heat to medium and add the butter to the same skillet. As it melts, scrape up any browned bits from the bottom. Add the minced garlic and cook for about 1 minute, stirring constantly, until fragrant and just barely golden.

Pour in the heavy cream and whole milk, stirring to combine. Bring to a gentle simmer and cook for 3-4 minutes, stirring occasionally, until the mixture thickens slightly.

Reduce heat to medium-low. Gradually add the parmesan cheese in three or four additions, whisking after each addition until completely melted before adding more. This prevents clumping. Taste and adjust seasoning with additional salt and pepper if needed.

Return the cooked tortellini and seared steak pieces (including any accumulated juices) to the skillet. Gently toss everything together using tongs until each piece is coated in the garlic cream sauce. Cook for about 2 minutes to heat everything through.

Serve immediately in shallow bowls, garnished with freshly chopped parsley, freshly cracked black pepper, and red pepper flakes if desired.