Red and White Potato Salad

• 2 pounds small new red potatoes (about 12)
• 1/4 cup red wine vinegar
• 1 tablespoon Dijon mustard
• 1/2 teaspoon salt
• 1 tablespoon finely chopped fresh dill or 1/4 teaspoon dried dill weed
• Freshly ground pepper, to taste
• 1 clove garlic, minced or pressed
• 1/2 cup olive oil
• 6 green onions, thinly sliced
• 1/4 cup chopped parsley
• 1/4 cup mayonnaise
• 1/4 cup sour cream
• 1 cup sliced radishes
• Hard-cooked egg slices, optional for garnish
• Fresh dill sprigs for garnish

Place potatoes in a large pot, add salted water to cover, and bring to the boil over high heat. Reduce heat to medium and cook until potatoes are tender, about 25 to 30 minutes. Drain and slice while warm. Place potatoes in a large bowl. In a small bowl, mix vinegar, mustard, salt, dill, pepper and garlic. Gradually whisk in oil until well combined. Pour oil mixture over warm potatoes, stirring gently to coat. Cover and refrigerate at least 2 hours. Gently mix in onion and parsley. Blend mayonnaise and sour cream until smooth, and fold into salad. Cover and refrigerate from 1 to 3 hours. Just before serving, gently mix in radishes. Garnish with egg slices and dill sprigs, if using.