Heat butter in a dutch oven over medium-high heat. Once melted and hot, add the onions and brown sugar. Cook about 10 minutes, stirring frequently, until softened. Add the Worcestershire sauce and wine, cooking until wine evaporates, about 10 minutes.
Preheat the the broiler to 550 degrees F.
To the dutch oven, add the mushrooms, garlic, salt and pepper; cook 3-4 minutes. Add chicken broth and bring to a boil. Add pasta, bay leaves, and thyme. Stir and cook for 10-15 minutes or until liquid has been soaked up by the pasta. Stir in the half and half; simmer an additional 5-10 minutes or until pasta are al dente.
Stir in the cayenne and half the gruyere cheese. Cook 2 minutes and then remove from the heat. Top with the remaining cheese and place under the broiler for 1-2 minutes until the cheese is melted. Serve warm, top with fresh thyme, if desired.