Heat olive oil in a large skillet over medium-high heat.
Season the beef with salt and pepper.
Sear on both sides for about 3 minutes per side, then transfer to the slow cooker.
Add the diced onion, carrots, and garlic to the slow cooker.
Stir in the crushed tomatoes, tomato paste, beef broth, red wine, oregano, basil, bay leaf, salt, black pepper, and red pepper flakes.
Cover and cook on low for 8 hours or high for 4–5 hours, until the beef is tender and easily shreds.
Remove the beef from the slow cooker and shred it using two forks.
Discard the bay leaf.
Return the shredded beef to the sauce and stir to combine.
Bring a large pot of salted water to a boil.
Cook the pasta according to package instructions until al dente.
Drain and toss with a little olive oil to prevent sticking.
Serve the shredded beef ragu over the pasta.
Sprinkle with grated Parmesan cheese.