Remove the meat to a shallow bowl using a slotted spoon. Remove carrots, potatoes, and onions, and place them into a serving dish. Set aside.
Skim fat, measure out 2 cups of hot cooking liquid, and reserve.
In a large bowl, combine butter and flour until smooth paste forms. Pour the hot cooking liquid into the butter-flour mixture and stir to thicken. Pour gravy into the slow cooker, stir to create a gravy, and cover and cook for another 20 minutes or so.