Step 1: Prep and Sear the Steak
Bring a large pot of salted water to a boil for the pasta. While it heats, prepare the steak. Pat the steak strips completely dry with paper towels—this is essential for a good sear. Season generously on all sides with salt and pepper. Heat the neutral oil in a large, heavy-bottomed skillet or Dutch oven over medium-high heat until shimmering. Add the steak strips in a single layer, working in batches if necessary to avoid overcrowding. Sear for 1-2 minutes per side, just until a deep brown crust forms. The steak will not be cooked through at this point. Transfer the seared steak to a clean plate and set aside. Do not wash the skillet.

Step 2: Cook the Pasta
Add the pasta shells to the boiling salted water. Cook according to package directions for al dente, usually 8-10 minutes. Once cooked, drain the pasta, reserving about 1 cup of the starchy pasta water. Set the drained pasta aside.

Step 3: Build the Aromatics and Roux
In the same skillet used for the steak, reduce heat to medium. Add 2 tablespoons of the butter. Once melted, add the diced onion and cook for 5-6 minutes, until soft and translucent. Add the minced garlic and cook for 1 more minute until fragrant. Push the onions and garlic to the side. Add the remaining 1 tablespoon of butter to the center of the pan. Once melted, sprinkle the flour over the butter. Cook, stirring constantly with a wooden spoon, for 1-2 minutes to form a pale golden roux (this cooks out the raw flour taste).

Step 4: Bloom the Paprika and Create the Sauce
Reduce heat to medium-low. Immediately add the smoked paprika, dried thyme, and tomato paste to the roux-onion mixture. Stir constantly and cook for 1 full minute. This critical step, called “blooming,” heats the spices in fat, unlocking their full flavor and aroma and turning the mixture a vivid red. Slowly, while whisking constantly to prevent lumps, pour in the beef broth. Increase heat to medium-high and whisk until the sauce is smooth and begins to thicken, about 2-3 minutes.

Step 5: Simmer and Enrich the Sauce
Whisk in the milk (or cream), Worcestershire sauce, and soy sauce. Bring the sauce to a gentle simmer. Allow it to cook, stirring occasionally, for 5-7 minutes until it has thickened to a creamy, gravy-like consistency that will coat the back of a spoon. Taste and adjust seasoning, adding more salt, pepper, or a pinch of cayenne if desired.

Step 6: Combine Steak, Pasta, and Sauce
Add the drained pasta and the seared steak strips (along with any accumulated juices) to the simmering sauce. Gently fold everything together until the pasta and steak are fully coated and heated through, about 2-3 minutes. If the sauce seems too thick, add splashes of the reserved pasta water until your desired consistency is reached. Remove the skillet from the heat.

Step 7: The Final Creamy Finish
Stir in the sour cream or Greek yogurt until fully incorporated and the sauce is luxuriously creamy. This off-heat addition prevents curdling. Finally, fold in most of the chopped parsley, reserving some for garnish. Serve immediately in shallow bowls, garnished with the remaining parsley and with lemon wedges on the side for a bright, citrusy squeeze that cuts through the richness.