Cuban Potato Salad with Scallion Vinaigrette

1 lb Small red potatoes, cut into 1/2" pieces
3 cup Cooked black beans
2 bn Scallions, white and part of green, sliced
1 cup Sour cream
1 tbl Freshly-squeezed lemon juice
1/2 tsp Salt
1/2 tsp Freshly-ground white pepper
1/2 cup Mayonnaise
1/2 bn Chives, thinly sliced

Bring a pot of salted water to a boil and cook the potatoes until tender, about 10 minutes. Set aside. When cool, transfer to a large bowl and combine with black beans. In a blender combine the scallions, sour cream and lemon juice. Pulse a few times to mix, then puree until smooth. Add salt, pepper and mayonnaise. Blend just to combine. Drizzle vinaigrette over salad, then toss until potatoes and beans are well coated. Garnish with thinly-sliced chives.