Serve this light ragout over pasta, polenta, or tortellini to make it a main dish.
Soak leeks in cold water for 5 minutes; lift out and drain. Repeat until no grit remains on bottom of bowl. Set aside.
Heat oil in a large skillet over medium-highheat. Add leeks and salt and sauteuntil leeks are tender, about 2 minutes. Stirin asparagus, then water. Simmer coveredfor 2 minutes. Add snap peas and radishes,cover, and simmer for 2 minutes more.
Stir in mustard until well combined, then swirl in butter and herbs. Serve immediately.
Serve sprinkled with Parmesan and drizzled with oil.