In a large skillet or Dutch oven, melt butter over medium heat. Add sliced onions and a pinch of salt. Cook, stirring occasionally, for 15-20 minutes until onions are deeply caramelized to a golden brown.
Add ground beef to the caramelized onions. Break up with a wooden spoon and cook until no longer pink, about 5-7 minutes. Add garlic and thyme during the last minute of cooking.
Pour in beef broth and Worcestershire sauce, scraping up any browned bits from the bottom of the pan. Bring to a simmer and let reduce slightly for 2 minutes.
Add uncooked egg noodles to the skillet, stirring to submerge in the broth. Cover and reduce heat to medium-low. Cook for 8-10 minutes until noodles are tender but still have slight bite.
Remove from heat and stir in sour cream until fully incorporated. Sprinkle Swiss cheese over the top, cover, and let sit for 2-3 minutes until cheese melts.
Season with additional salt and pepper if needed. Garnish with fresh herbs if desired and serve hot.
Notes
This dish is perfect for a cozy dinner. Feel free to experiment with different cheeses or add mushrooms for extra flavor.