In the PPC-XL, add the potatoes, water, onion, butter, salt, and pepper. Cover and set the vent to closed. Press the Soup/Stew button for a time of 12 minutes. Release pressure and add the milk; stir. Serve with crackers. Stove Top: In a large sauce pan on medium-high heat, add the potatoes, onion, butter, water, salt, and pepper. Cover and bring to a boil. Cook for about 30 minutes or until the potatoes are tender enough to cut with a fork. Remove from heat and add the milk; stir. Serve hot with crackers.