Whole grain mustard and a variety of fresh herbs add wonderful taste and texture to this summery potato salad.
Put the potatoes into a large pot of salted water, bring to a boil, and then cook for 15 to 20 minutes, until they are just cooked through. Drain in a colander and place a towel over the potatoes to allow them to steam for 10 more minutes. As soon as they are cool enough to handle, cut the potatoes into 1-inch pieces and place in a bowl. Toss gently with the lemon juice, stock, vinegar, mustard, salt and pepper. Allow the liquids to soak into the warm potatoes before proceeding.
Combine the olive oil, scallions and herbs in a blender and puree until just combined. Toss the herbs and oil with the potatoes and serve warm or cold.