Heck of a "Potato Salad"

True, there are no potatoes visible in this photo. That's because the arugula/smoked salmon/sliced apple salad sits atop the potato/sour cream salad below it. This is an elaborate recipe but it makes a large amount that can easily serve 6-8 people, and it was a huge hit as a side dish at my July 4th cookout.

Recipe: Potato Salad topped with Arugula/Smoked Salmon Salad

Serves 6-8
Ingredients:
For the potato salad: 
12 ounces small red or white potatoes
1 cup sour cream
2 T Dijon mustard
Salt and freshly ground black pepper
2 T capers, rinsed
For the arugula salad:
3 cups arugula or arugula mixed with microgreens
6 ounces smoked salmon, cut into bite-size pieces

1 Granny Smith apple, cored and very thinly sliced
1/2 cup vinaigrette made with lemon juice, olive oil and cider or sherry vinegar

Instructions:
Put the potatoes in a large saucepan and cover with cold water. Bring to a boil and cook until just tender, about 6-7 minutes. Drain and run potatoes under cold water to stop the cooking and cool them. Drain again, then cut potatoes into bite size pieces and place in a large bowl. Mix the sour cream and mustard together in a small bowl, then gently stir mixture into the potatoes. Season with salt and pepper and stir in capers. Set aside.
In another bowl, toss the greens with the salmon and apple, then add the vinaigrette.
Spoon the arugula salad over the potatoes, bring to table and serve.