How to Make It
In a large bowl, whisk the mustard with the vinegar. Whisk in the canola oil in a thin stream and season with salt and pepper.
Bring 2 medium saucepans of salted water to a boil. Add the potatoes to one and cook for 20 minutes. Simultaneously, cook the asparagus and leeks in the other saucepan for 5 minutes. Drain and pat dry; add to the vinaigrette. Drain the potatoes and slice 1/2 inch thick; add to the bowl. Add the chives, season with salt and pepper and gently toss the salad. Serve warm.