In a large pot, cover potatoes with water and bring to a boil over high heat. Simmer on medium-high heat until the center of the potatoes are tender when pricked with a fork, about 25 minutes. Drain, and return potatoes to pot.
Meanwhile, heat butter and olive oil in a large skillet over medium heat. Stir in onions, sprinkle with salt, and cook 5 minutes. Reduce heat to medium low, and cook, stirring occasionally, until onions are a deep golden brown, about 20 minutes. Stir in brown sugar.
Pour whipping cream over the potatoes, and mash with a large fork or potato masher. Stir in sour cream, cream cheese, soy sauce, Parmesan cheese, bouillon granules, and dried parsley. Stir in caramelized onions, and season with black pepper. Mix with an electric mixer until smooth. Reheat briefly over low heat, and serve.