2 pounds red potatoes, cut into 1-inch chunks
1 pound sweet potatoes, peeled and cut in 1-inch chunks
1/4 cup red wine vinegar
1 tablespoon spicy brown mustard
1 1/4 teaspoons salt
1/2 teaspoon pepper
1/2 cup reduced-fat mayonnaise
1/4 cup 2% milk
2 celery ribs, chopped
1 small red onion, chopped
1/3 cup minced fresh parsley
Place the red potatoes in a large saucepan and cover with water; bring to a boil. Reduce heat; cover and cook for 2 minutes. Add sweet potatoes; return to a boil. Reduce heat; cover and cook 8-10 minutes longer or until potatoes are fork-tender.
In a large bowl, whisk the vinegar, mustard, salt and pepper. Drain potatoes; add to vinegar mixture and stir gently to coat. Cool.
In a small bowl, combine mayonnaise and milk. Stir in the celery, onion and parsley. Gently stir into cooled potato mixture. Serve immediately or cover and chill.