Pat short ribs dry with paper towels, then season with salt and black pepper on all sides.

Heat oil in a large Dutch oven over medium-high heat. Once hot, add the short ribs in a single layer and sear each side for about 2 minutes, until nicely browned. Work in batches if needed to avoid overcrowding. Transfer to a plate and set aside.

Reduce heat to medium, Add the onions, carrots, celery, and garlic, and saute for 2 minutes. Add the baby bella mushrooms and cook for another 2 minutes. Stir in the tomato paste and cook until well combined.

Pour in red wine to deglaze the pot, scraping up any browned bits. Tie thyme and rosemary together using kitchen twine. Add to pot along with bay leaves, parmesan rind, 1/2 tsp salt, 1/4 tsp black pepper, and beef bouillon paste (if using). Pour in the crushed tomatoes and beef broth. Stir well, bring to a boil, then reduce the heat to low. Cover with a lid and simmer for 2 1/2 hours, stirring occasionally. (If the sauce reduces too much, add a splash of broth or water.)

Remove the short ribs from pot and place on a cutting board. Discard the herbs, bay leaves, and parmesan rind. Remove and discard the bones, then use two forks to shred the meat into bite-sized pieces. Return the shredded beef to the pot and stir to combine. Simmer uncovered for 15-20 minutes, until the Ragu thickens. Add the oyster mushrooms to pot and cook another 5 minutes.

While the Ragu finishes thickening, cook the pasta according to package directions until al dente. Once the pasta is done cooking, add it directly to the pot with the Ragu. Toss and cook together for 1-2 minutes, until the pasta is evenly coated. Add a splash of pasta water if the sauce feels too thick. Season with more salt if needed. Stir in chopped parsley.

Plate the pasta and top with freshly grated parmesan cheese. Serve warm and enjoy!