Sprinkle salt and pepper all over roast, place fat side up in dutch oven or roaster; bake uncovered for 1 hour at 375f degrees.
Reduce heat to 325f degrees, sprinkle roast with desired seasoning; add 1/2 cup water or broth to roaster, cover and bake for 1 hour.
Remove the roaster from the oven; add 3/4 cup water or broth to roaster, add the potatoes carrots, onions and mushrooms, sprinkle them with salt and pepper; cover and roast for another hour or until veggies are tender.
Remove roast to platter and slice; surround with veggies, cover with foil and keep warm.
Add cornstarch to cold water, whisk and add to roaster, whisk while bringing to boil, simmer for 5 minutes or until thickened; ladel over roast and veggies; serve and enjoy.