Heat a wide skillet over medium high heat. Generously salt (about 1-1/2 to teaspoons) and pepper (about 1 teaspoon) all sides of the roast.
Add oil to skillet and swirl around to coat the bottom. Add the roast to the pan and do not move it for about 2 minutes. Flip it over and repeat on all other sides. Transfer the roast to a slow cooker.
Keep the hot pan on the stove and add the water and beef base. Stir, breaking up any brown bits on the pan until the beef base is dissolved. Pour the liquid into the slow cooker.
Sprinkle the roast with the thyme. Add the bay leaf. Dump the onion soup mix directly on the roast (not in the water). Rub the powder into the exposed roast. Some of the soup mix will fall in the water, but that is ok.
Cover the slow cooker with the lid and cook on low for 8 to 10 hours.
About 3 hours before the roast is finished, add the carrots.
Remove the roast to a cutting board and let it rest while you prepare the gravy.
Use a fat separator to separate the fat from the drippings. Discard the fat and add all of the drippings to a medium saucepan. Turn the heat to high.
Place enough very cold water in a measuring cup so that there will be about 4 cups of liquid total. Whisk in flour, making sure that you get rid of all of the lumps.
When the drippings have heated to a boil, slowly stir in the flour mixture while stirring. Add the beef base and bring the mixture to a low boil. Let the gravy simmer for 3 to 5 minutes until it has thickened.
Shred the roast with two forks and serve with the gravy.