Place potatoes in a small saucepan, cover with water and add 1 teaspoon salt; bring to a boil. Cook over medium heat just until tender, 5 to 6 minutes. Add peas, cover and cook for 2 minutes more. Drain, add butter, 1/2 teaspoon pepper and mint. Heat for 1 minute and toss gently. Season to taste with salt and pepper.