Bring a large pot of well-salted water to a boil
Pat the beef completely dry with paper towels, Let it sit at room temperature for about 15 - 30 minutes. I like to keep the fat on my steak, as it adds extra flavor to the dish. After letting your beef sit, season generously with demoed crystal kosher salt
Heat a large heavy skillet over medium-high heat. Once hot, add the avocado oil. add half the beef in a single layer. Do not overcrowd the pan. Let it sear undisturbed for 1–2 minutes until deeply browned, then flip and cook briefly on the other side. The beef should still be slightly pink inside. Transfer to a plate and repeat with the remaining beef
Reduce heat to medium. Add the butter. Add the onions with your 1 tbsp of sugar and cook them in the residual fond left from the steak, about 5 minutes, stirring occasionally, until soft and lightly golden
Add the mushrooms. Spread them out and let them sit undisturbed for a few minutes before stirring. Cook until their moisture releases and evaporates, about 10 minutes
Stir in the garlic and cook for 30 seconds. Add the garlic powder, onion powder, paprika, white pepper, black pepper, and tomato paste, salt, pepper and cook for 1–2 minutes, stirring until the tomato paste darkens slightly
Add the Dijon mustard and stir to combine. Pour in about 1/2 cup of the beef stock to deglaze the pan if needed, scraping up all the browned bits. Let it reduce slightly for about 3 minutes on medium heat, then add the remaining stock, Worcestershire sauce, and thyme. Simmer gently for 5–7 minutes until the sauce thickens slightly
Meanwhile, cook the pasta just shy of al dente. Reserve 1/2 cup pasta water before draining
Reduce the heat under the sauce to low. Stir in 1 teaspoon apple cider vinegar. Taste and add the second teaspoon gradually if more brightness is needed. Stir in the sour cream gently until smooth and silky. If the sauce feels too thick, add a splash of reserved pasta water. But if youre happy with your sauce, the pasta water isn't necessary
Taste and adjust salt if necessary
Return your beef to the skillet. Let it simmer gently for 2–3 minutes, just until the beef is warmed through. Dont boil once the sour cream is added
Toss the pasta directly into the sauce or spoon the stroganoff generously over it. Finish with chopped parsley, freshly grated parm, and additional freshly cracked black pepper to taste