Chef Eberhard Mueller likes to celebrate the bounty of his Long Island garden by including a wide range of herbs and vegetables in his salad.
Trim the roots and tough tops off the leeks, leaving about 6 inches of white and pale green; rinse them very well to remove any grit between the leaves. Scrape baby carrots. Cut the bottoms off asparagus to leave the tips about 4 inches long. Trim tops off beets, leaving about an inch of stem.
Prepare an ice-water bath. Bring a large pot of salted water to a boil over high heat. Cook the peas in the water until they are bright green and tender. Immediately remove with a skimmer or large slotted spoon and transfer to ice water. Lift out and drain well; set aside. Repeat with the remaining vegetables: Cook leeks and carrots until just tender, about 3 minutes; cook asparagus until tender, 3 to 5 minutes; cook baby beets until tender, 20 to 30 minutes. Peel the beets (the skins will slide off), and quarter them.
Rinse mache well in a generous amount of cold water. Dry in a salad spinner; set aside. Peel the kohlrabi and cut into thin julienne strips on a Japanese mandoline. Remove stalks and outer leaves from fennel, and shave finely using mandoline.
Assemble the salad: Toss mache with 1/4 of the vinaigrette dressing, and mound it on a large platter. Toss peas, leeks, carrots, asparagus, kohlrabi, and 2/3 of the sorrel with 2/3 of the remaining dressing. Arrange the mixed vegetables over the mache. Toss the beets with the remaining dressing, and scatter them on top. Garnish with the remaining sorrel.