In a large pot, heat the olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, for about 10-15 minutes until they are caramelized and golden brown.
Add the minced garlic, dried thyme, and sugar to the pot. Cook for an additional 1-2 minutes until fragrant.
Pour in the vegetable broth and soy sauce, then bring the mixture to a boil.
Stir in the uncooked pasta, reduce the heat to a simmer, and cover the pot. Cook for about 10-12 minutes, or until the pasta is al dente, stirring occasionally to prevent sticking.
Once the pasta is cooked, stir in the heavy cream and half of the Gruyère cheese. Mix well until the cheese is melted and the sauce is creamy.
Season with salt and pepper to taste. Serve hot, topped with the remaining Gruyère cheese and chopped parsley for garnish.