Potato Salad with Avocado and Arugula

A wonderful different potato salad.  I love the avocado in it and the Arugula gives it some bite.  You can peel the potatoes but I prefer the skin on.  From Food and Drink 2011

3 lbs (1.5 kg) small new potatoes
3/4 cup light sour cream
3/4 cup light mayonnaise
1 1/2 tsp salt
1/4 tsp freshly ground black pepper
1/2 cup finely diced red onion or thinly sliced green onions or snipped chives
1 large or 2 small ripe avocados
3 to 4 cups baby arugula, coarsely chopped
Grape tomatoes

1. Generously cover potatoes with cold water in a large saucepan.  Bring to a boil over high heat.  Reduce heat to maintain a gentle boil; cook covered for 20 to 25 minutes or until just tender when pierced with a  skewer.  Drain; cool until able to handle.
2. Meanwhile, in a large mixing bowl, stir sour cream with mayonnaise, salt and pepper.  Stir in red onion.
3. Cut warm potatoes into bite size chunks; add to dressing as cut.  Using a large spoon or spatula, gently mix potatoes by lifting up from bottom of bowl and turning over.  To aid in rapid cooling, make a well in salad centre if in a bowl or spread out in a large metal pan.  Cover with plastic wrap; refrigerate several hours or up to a day until cold.
4. When ready to serve, dice avocados.  Stir potato salad gently; fold in avocado until just mixed.  Fold in arugula.  Garnish with additional red onion or halved grape tomatoes.