Steam halved potatoes in a metal steamer basket until fork tender, then remove from steamer and add asparagus. Steam a few minutes more, until asparagus turns bright green and is fork tender, or to desired level of tenderness. Drain. Place in large serving bowl.

Place parsley, mint, chives, olive oil, mustard, vinegar, and ½ teaspoon sea salt in a food processor or blender and blend until the leaves are just small flecks (it will resemble a thin pesto). Pour over steamed potatoes and asparagus and gently toss to coat. Add fresh ground pepper and a few sprinkles of sea salt, to taste. Let sit 10 minutes to let flavors marry. Serve while warm.