Bring a large pot of well-salted water to a boil. Add the short pasta and cook according to package directions until just al dente. Before draining, scoop out about 1/2 cup of the starchy pasta water and set it aside, then drain the pasta.

While the pasta cooks, pat the steak dry with paper towels. Slice it into thin strips against the grain, then season the strips all over with kosher salt, black pepper, and paprika.

Heat the olive oil and unsalted butter in a large skillet over medium-high heat. When the fat is hot and shimmering, add the seasoned steak strips in a single layer, working in batches if needed, and sear for about 1–2 minutes per side until browned on the outside but still slightly pink inside. Transfer the seared steak to a plate and set aside, leaving any juices in the skillet.

Reduce the heat to medium. In the same skillet, add the minced garlic and cook for about 30 seconds, stirring constantly, just until fragrant and lightly golden around the edges. Avoid letting it brown too much.

Pour in the heavy cream and low-sodium beef broth. Stir in the Dijon mustard and red pepper flakes, if using. Bring the mixture to a gentle simmer and let it cook for 3–4 minutes, stirring occasionally, until it starts to slightly thicken.

Add the grated Parmesan cheese to the skillet and stir until it melts smoothly into the sauce. If the sauce seems too thick, splash in a little of the reserved pasta water, a tablespoon at a time, until it reaches a silky, pourable consistency.

Add the drained pasta to the skillet and toss gently until every piece is coated in the creamy sauce. Return the seared steak strips and any accumulated juices on the plate to the pan, and toss again just until the steak is warmed through.

Turn off the heat, sprinkle the chopped fresh parsley over the creamy steak pasta, and give it a final gentle stir. Taste and adjust the seasoning with a pinch more salt or black pepper if needed, then serve right away while hot and creamy.