Place the pork roast in a medium baking dish. Season red potatoes with salt and pepper, and arrange around the roast. Place sweet potatoes and cinnamon in a resealable plastic bag, and shake to coat. Arrange sweet potatoes around the roast. Place apple over the roast and potatoes. Top with butter slices. Seal baking dish tightly with foil.
Cook 1 1/2 hours in the preheated oven, or until the internal temperature of the pork has reached 145 degrees F (63 degrees C).
In a medium saucepan over medium heat, blend the milk, water, chicken bouillon, beef bouillon, and cornstarch until the bouillon cubes are dissolved and the mixture is thickened. Serve with the pork roast and potatoes.