First, melt butter in a saucepan over medium heat. Stir in the onion and cook until the onion has softened and turned translucent about 5 minutes. While the onions are cooking, place the diced potatoes, carrots, water and chicken soup base in another pot and bring to a boil. Cook until vegetables are tender, about 10 minutes. Do not overcook. Season with ground black pepper to taste.