Cut the beef into 3-inch chunks and season with salt and pepper.
Warm 2 tablespoons of the olive oil in a large Dutch oven (or oven-safe heavy-bottomed pot) over medium-high heat. Once you can feel the heat when you hold your hand 6 inches above the pot, place the roast pieces in the pot. Brown the pieces on all sides, 2-3 minutes per side. (To get a good sear don't overcrowd the meat, you can sear the meat in batches). Don't skip this step. We are adding layers of flavor here. Once the roast is nicely seared with a good crust, remove it from the Dutch oven and place it in your slow cooker. (Use a 5 quart or larger slow cooker).
Add the remaining 2 tablespoons of olive oil and the sliced onions to the Dutch oven and cook until the onions are translucent, 3 to 4 minutes. Add the garlic and cook for about 30 seconds. Sprinkle in the seasoning blend and add the Worcestershire sauce. Stir to combine. Pour in the wine (or additional beef stock of juice). Deglaze the pan by scraping up the browned bits at the bottom of the pan with a wooden spoon or spatula as it bubbles. Pour in the beef stock. Stir to combine, and then add the contents of the pot into the slow cooker. Cover and cook for 5 hours on high (or 10 hours on low). Add the carrots and potatoes halfway through the cook time.
Remove the roast and vegetables from the slow cooker and place them on a serving dish. Tent with foil. Ladle the cooking liquid into a 4-quart saucepan and bring it to a boil over medium-high heat. Combine the cornstarch and water in a small bowl and whisk until completely smooth to create a slurry. Pour the slurry into the pot and stir. Boil the gravy until thickened, 3 to 5 minutes. Taste for seasoning, and add salt and pepper as necessary.
Serve the pot roast and veggies with the gravy on the side.