1-First, heat 1 tablespoon olive oil in a large pot over medium-high heat. Pat the chuck roast dry with paper towels and season generously with salt and pepper, then sear the roast for 4-5 minutes per side until browned and transfer it to the slow cooker.

2-Next, add the remaining 1/2 tablespoon olive oil to the pot and sauté the onions for 2 minutes, then add garlic and cook for 30 seconds before pouring this mixture over the roast in the slow cooker.

3-Now, deglaze the pot by adding beef broth, Worcestershire sauce, thyme, and rosemary. Scrape up the browned bits from the bottom, let it simmer for 15 seconds, and pour the mixture over the roast and onions in the slow cooker.

4-Layer the whole potatoes and carrots over the onions, season with salt and pepper, cover, and cook on low heat for 8-9 hours until everything is tender.

5-Once done, remove the roast and vegetables, shred the roast while discarding any fat, and halve the potatoes if you like. Strain the broth into a saucepan for gravy.

6-For the gravy, whisk the cornstarch mixture until smooth and stir it into the saucepan, heating over medium-high heat until it thickens, which takes about 30-60 seconds.

7-Finally, plate the roast and vegetables, pour the gravy on top, and garnish with parsley. The total time is about 8 hours and 25 minutes, with 25 minutes of prep and 8 hours of cooking, so plan ahead for that slow simmer.