Begin by placing your purple potatoes in a large pot, covering them with water. Bring to a boil over medium-high heat, then reduce to a gentle simmer. Cook for about 15-20 minutes until fork-tender.

While the potatoes are cooling, thinly slice the radishes and chop the green onions into small pieces.

In a medium mixing bowl, combine sour cream, olive oil, and lemon juice. Add salt and pepper to taste. Whisk until well blended.

In a large mixing bowl, gently toss chopped potatoes, sliced radishes, and green onions. Drizzle the creamy dressing over and fold gently.

Cover with plastic wrap and refrigerate for about 30 minutes to deepen the flavors. Stir before serving.