In a large skillet or Dutch oven, heat the olive oil and butter over medium heat.
Add the sliced onions and sprinkle with a pinch of salt. Cook, stirring occasionally, for about 15-20 minutes, until the onions are caramelized and golden brown.
Add the minced garlic to the onions and cook for another minute until fragrant.
Increase the heat to medium-high and add the sliced beef to the skillet. Season with salt, pepper, thyme, and Worcestershire sauce. Sear the beef for about 5-7 minutes until browned, stirring occasionally.
Pour in the beef broth and bring the mixture to a simmer. Reduce heat to low and let simmer for 15-20 minutes, allowing the flavors to blend.
While the beef mixture simmers, cook the egg noodles according to package instructions until al dente. Drain and set aside.
Once the beef mixture has thickened slightly, add the cooked noodles to the skillet, stirring to combine.
Preheat your oven's broiler.
Transfer the beef and noodle mixture to a baking dish, sprinkle the shredded Gruyère cheese on top, and place under the broiler for 2-3 minutes, or until the cheese is melted and bubbly.
Remove from the oven, let cool for a minute, and garnish with chopped parsley before serving.