If you're serving the meatballs with mashed potatoes, fill a medium pot with water about 3/4 full and cover with a tight-fitting lid. Heat this over high heat to bring to a boil. You want just enough water to cover the potatoes during cooking. While the water is heating, peel and dice the potatoes. Remember: Smaller potatoes cook faster thank large chunks. Add these to the pot even if the water is not boiling yet. Be sure to salt the water liberally.