Prep your beef properly. Pat the meat dry with paper towels (crucial for good browning!), then season generously with salt and pepper. If the meat is cold from the fridge, let it sit at room temperature for about 15 minutes before cooking.
Get your pasta water going. Fill a large pot with salted water and bring to a boil. You want this ready when you need it.
Sear the beef to perfection. Heat 1 tablespoon butter and the olive oil in a large skillet over medium-high heat until shimmering. Working in batches (don't crowd the pan!), add the beef strips in a single layer and cook for about 1 minute per side until browned but still pink inside. Remove to a plate and set aside. This quick sear keeps the meat tender!
Create your flavor base. In the same skillet, add the remaining tablespoon of butter. Add onions and cook for 2-3 minutes until they begin to soften. Add the mushrooms and cook until they release their moisture and begin to brown, about 5-7 minutes. Don't rush this step – those caramelized mushrooms are flavor gold!
Add garlic and cook until fragrant, about 30 seconds. Don't let it burn or it'll taste bitter!
Make the sauce. Sprinkle the flour over the mushroom mixture and stir constantly for 1 minute. Slowly pour in the beef broth (and wine, if using), stirring constantly to prevent lumps. Add the Worcestershire sauce and Dijon mustard, then bring to a simmer.
Cook your noodles. While the sauce simmers, add the egg noodles to the boiling water and cook according to package directions until al dente, usually about 5-7 minutes.
Finish the sauce. Reduce heat to low and let the sauce simmer for 5 minutes until it thickens slightly. Return the beef (with any accumulated juices – that's flavor!) to the skillet and heat through, about 1-2 minutes. You don't want to overcook the beef!
Add the magic. Remove the skillet from heat and let it cool for just a minute. Then stir in the room temperature sour cream until fully incorporated. This cooling moment helps prevent the sauce from curdling. Season with salt, pepper, and paprika (if using).
Drain the noodles but don't rinse them! That starch helps the sauce cling to the pasta.
Serve immediately. Place noodles in bowls, top with the stroganoff, and sprinkle with fresh parsley. Get ready for the compliments!