Remove roast from fridge an hour before cooking. Season all sides with salt and pepper.
Preheat oven to 300 degrees.
Heat oil in dutch oven over medium heat. Brown sliced onions until nicely carmelized. Move to side, then add the roast to hot dutch oven to seer all sides just until browned. Then add 5 cups of water or beef stock and place lid on dutch oven. Bring to a quick boil then remove from stove and place in 300 degree oven for approximately 1 1/2 - 2 hours or until meat temp reaches 170 degrees.
When roast is done, remove roast and onions to platter. Place dutch oven on stove high heat and boil liquid, reducing it until thick and rich.
*Optional: To thicken sauce mix 2 tablespoons of cornstarch into 1/2 cup water. Using a whisk, stir the slurry into the liquid, stirring constantly for a few minutes. Remove from heat, sauce will thicken as it rests.
Lastly, spoon thick sauce with onions over the roast, then cut roast into slices and serve.