Put potatoes, cheddar, sour cream and cream cheese in mixer or food processor - process til mashed potatoe consistancy.
Melt butter - saute mushrooms until they give up their moisture. Add in Whrchestershire sauce. Mix in flour - stir constantly for 2 minutes. Add broth, stir til boiling - turn to simmer and allow to thicken somewhat.
Mix diced roast, carrots, drained corn and mushroom gravy together.