Place the potatoes and sweet potatoes in a large pot with enough water to cover. Bring to a boil. Cook about 15 minutes, until tender but firm. Remove from heat, and drain.
Preheat the oven broiler.
In a large bowl, mash the potatoes. Gradually mix in butter, heavy cream, chicken bouillon, brown sugar, and pepper. Transfer the mixture to a medium baking dish, and top with Monterey Jack cheese.
Broil uncovered in the preheated oven 10 minutes, or until the cheese is melted and lightly browned.
