Bring a large pot of salted water to a boil. Cook the pappardelle until al dente according to the package instructions. Reserve ½ cup of the pasta water and drain.
Heat olive oil in a large skillet or Dutch oven over medium heat. Add onions, carrots, and celery, and cook for 6–8 minutes until soft and fragrant.
Stir in garlic and cook for 1 minute. Add chopped portobello mushrooms and sauté for 8–10 minutes until their moisture has released and evaporated, and mushrooms are browned.
Stir in the tomato paste and cook for 2–3 minutes to deepen the flavor. Pour in the red wine to deglaze the pan, scraping up any brown bits. Simmer for 3–4 minutes until wine reduces slightly.
Add crushed tomatoes, oregano, thyme, and vegetable broth. Stir well, bring to a gentle simmer, and cook uncovered for 15–20 minutes until the ragu thickens. Season with salt and pepper to taste.
Add the cooked pappardelle and a splash of pasta water to the ragu. Toss gently until the pasta is fully coated and the sauce clings to the noodles.
Top with fresh parsley and grated Parmesan or Pecorino if desired. Serve hot.