COOK IT.
Preheat grill/smoker to 375°F. Place a dutch oven over the open sear plate on the bottom rack to preheat.
In a blender, add broth, garlic, and beef broth until combined well. Set aside.
Once grill is preheated, add butter to the cast iron and let melt. Add in dry pasta and toast for 2-3 minutes, stirring well. Add chopped mushrooms and onions. Sauté for 3-4 minutes until the veggies are cooked through.
Add blended broth mixture and heavy cream to the cast iron. Stir to mix.
In a small bowl, make a 'slurry' by combining corn starch and water. Add this to the soup to thicken it.
Bring soup to a simmer and cook for 10 minutes or until the noodles are soft. You may have to adjust your grill's seat place to maintain a steady simmer.
After 10 minutes and once soup has thickened, stir in pepper, salt and thyme.
Remove soup from the grill and serve hot with parmesan cheese and crispy fried onions.