Pre-heat oven to 350 degrees. In roaster pan, brown roast in oil. Add broth. Spread horseradish over roast; sprinkle with onion, salt and pepper. Cover and bake 2 hours or until tender, basting frequently. Remove roast from the pan; let stand for 10 minutes.
Meanwhile, measure the pan juices; add water to equal 2 cups. Return to sauce
pan. Combine flour and cold water until smooth; stir into pan juices.
Bring to a boil; cook and stir for 2 minutes. Add additional water if a
thinner gravy is desired. Slice roast; serve with gravy.