In a large skillet, heat the olive oil and butter over medium heat. Add the sliced onions and cook, stirring occasionally, until caramelized, about 15-20 minutes. Add the minced garlic in the last minute of cooking.
Once the onions are caramelized, push them to the side of the skillet and add the beef stew meat. Season with salt, pepper, and thyme. Brown the beef on all sides, about 5-7 minutes.
Pour in the beef broth, stirring to combine. Bring the mixture to a simmer, cover, and let it cook for 25 minutes, until the beef is tender.
Meanwhile, in a pot of boiling salted water, cook the egg noodles according to package instructions until al dente. Drain and set aside.
Once the beef is tender, add the cooked noodles to the skillet and stir well to combine all ingredients.
Preheat your oven’s broiler.
Transfer the beef and noodle mixture to a baking dish, sprinkle the top with shredded Gruyère cheese, and place under the broiler for about 3-5 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let cool slightly. Garnish with fresh parsley before serving.