In a hot pan, sear the roast on each side for about a minute.
Add roast to the crock pot with the 1/2 chopped onion, 2 bullion cubes (crushed) and 2 cups of water. You want to make sure you are covering most of the roast, so adjust the amount of water to the size of your roast and crock pot.
Set the crock pot on high and cook for 1 hour. Then reduce the temperature to low.
After the roast has been cooking for 3 hours, add the carrots and the potatoes. Cook on low for another 3 hours or until the roast falls apart.