Pat the beef dry, sprinkle it generously with salt and pepper.
Heat 1 tbsp olive oil in a heavy-based pot on high. Sear the beef pieces on all sides until browned, about 3-5 minutes total, then transfer to a plate.
Reduce heat to medium-low. Add the remaining olive oil, garlic, and onion, sauté for 2 minutes.
Mix in the carrots and celery, cooking slowly for 5 more minutes until softened.
Transfer everything into your slow cooker, including the beef and its juices. Add crushed tomatoes, tomato paste, bouillon cubes, water, thyme, and bay leaves.
Set the slow cooker to low, cover, and cook for 6-8 hours (6 hours gives a firmer texture; 8 hours is ultra-tender).
Once done, remove the beef and shred with two forks. Return the beef to the sauce in the slow cooker.
Cook the pasta according to package instructions, draining 1 minute early.
Heat a large skillet with 5 cups of ragu sauce, toss in the cooked pasta, then add 3/4 cup pasta water. Toss for 1-2 minutes to emulsify.
Serve immediately with grated parmesan and parsley, if desired.
