Boil potatoes until tender, drain and reserve. Return the pot to the stove top over medium heat. Add butter and bananas to the pot. Cook bananas 5 minutes and add the juice of 1 orange to the pot, reserve the zest. Allow the juice to cook out, 1 minute. Add potatoes to the pot and the stock and sugar. Mash potatoes, banana, stock and sugar together until well combined. Season with nutmeg, salt, pepper and orange zest, to your taste. Mash to combine spices and serve.