Melt 2 tbsp butter in a large, deep skillet over medium-low heat. Add 1 sliced yellow onion and cook for 10–12 minutes, stirring occasionally, until soft and deeply golden. Transfer the onion to a plate.
Increase the heat to medium-high and melt the remaining 1 tbsp butter. Add 12 oz sliced cremini mushrooms and cook for 7–10 minutes, stirring only occasionally. Once most of their moisture has evaporated, season with salt and freshly ground black pepper to taste. Continue cooking until deeply browned, then transfer the mushrooms to the plate with the onion.
Add 1 lb ground beef to the cleared skillet and season with 1 tsp Lawry’s seasoned salt. Cook for 5–7 minutes, breaking the beef into bite-sized crumbles, until browned. Drain any excess grease, leaving about 1 tbsp in the skillet.
Reduce the heat to medium. Add 3 minced garlic cloves and cook for 30 seconds. Sprinkle 1 tbsp flour over the beef and cook for 1 minute, stirring until no dry flour remains.
Pour in ¼ cup Sauvignon Blanc, scraping up the browned bits from the bottom of the skillet. Simmer for 1–2 minutes, until the wine has nearly evaporated.
Stir in 3 cups beef broth and 1 tsp beef Better Than Bouillon. Bring the mixture to a gentle boil.
Add 8 oz wide egg noodles and press them into the broth. Reduce the heat to a gentle simmer, cover, and cook for 5 minutes, stirring once or twice. Uncover and continue cooking for 2–4 minutes, until the noodles are just al dente. Add another splash of beef broth if the skillet becomes dry before the noodles are tender.
Return the caramelized onion and browned mushrooms to the skillet. Stir in 1 tbsp Worcestershire sauce and simmer for 1–2 minutes.
Remove the skillet completely from the heat. Temper ½ cup sour cream with a few spoonfuls of the warm sauce, then gently stir it into the stroganoff. Stir in 2 tbsp chopped fresh parsley.
Let the stroganoff rest for 3–5 minutes to allow the sauce to thicken. Taste and adjust the salt and pepper as needed, then serve with freshly grated Parmesan.