Mashed Potato Salad

INGREDIENTS

• 5 red potatoes
• 5 Yukon Gold potatoes
• 2 tablespoons butter
• salt and pepper to taste
• 1/2 cup mayonnaise
• 1/2 cup prepared mustard
• 1/2 cup sour cream
• 1 stalk celery, finely chopped
• 1 red onion, finely diced
• 2 small sweet pickles, finely chopped
• 1 green bell pepper, chopped