Cut beef into 4 pieces. OPTIONAL FOR ADDED FLAVOUR: Heat olive oil in a large pan or skillet over medium-high heat. Sear each piece of beef on both sides until browned (about 5 minutes each side). Transfer each piece to your 6qt slow cooker bowl as soon as they are seared.
You should have left over oil in the pan (or skillet) from the beef. If not, add 1 tablespoon of (extra) oil to the pan. Fry the garlic until fragrant (about 30 seconds). Add the onion and fry until transparent. Add the garlic/onion mixture over the beef in the slow cooker, plus all remaining ingredients (except for the cornstarch/water mixture).
Cover and cook on LOW for 7-8 hours, or HIGH for 4-5 hours.The beef is ready if it falls apart easily when pulled apart with two forks.
NOTE: If you desire a thicker sauce, stir the cornstarch/water mixture into the slow cooker. Cover and cook on high heat for an additional 30 minutes and allow to thicken.
Shred the beef into pieces; mix through the sauce. Serve over pasta, rice, polenta, zucchini noodles or spaghetti squash.
Notes
IF SERVING WITH PASTA: In the last 15 minutes of cooking time, boil pasta in salted water following packet instructions. Drain, reserving ½ cup pasta water. Pour the reserved water back into the pasta along with 2 cups of cooked ragu. Stir until the sauce is thick enough to coat the pasta. Serve with parmesan cheese and (extra) chopped parsley, if desired.