How to Make It
In a large bowl, whisk together lemon juice, Dijon mustard, olive oil, kosher salt, and freshly ground black pepper. Set aside. Bring a large pot of generously salted water to a boil. Cook asparagus spears until fork-tender, about 4 minutes; drain. Add to the bowl, along with 1 thinly sliced shallot. Toss to coat.