In large Dutch oven pan pour small amount of Catalina dressing. Brown both sides of the roast in the dressing. After roast is browned, turn down the heat and add onion slices on to the roast. Add rest of the dressing and enough water to cover 3/4 of the roast. Add potatoes, and carrots.
Let cook on top of stove at a low to medium heat, you can keep adding water to keep roast covered. Cook about 1 1/2 hrs. or until carrots are tender.
Remove roast, potatoes, and carrots from pan. Put the flour into a small container with a lid add enough water to make a paste like. Slowly add to remaining liquid in the pan stirring as you add. This makes the gravy.