Seared Asparagus with Lemon-Dill Vinaigrette

1 bunch thin asparagus, trimmed

Juice of 1 lemon

1 teaspoon whole-grain mustard

1/4 cup olive oil

1/4 cup chopped dill

Salt and pepper

Heat a cast iron skillet over high heat until smoking. Working in batches, cook asparagus until blackened in spots and tender, about 1 minute per side. Transfer to a plate. 

In a mixing bowl, whisk together lemon juice and mustard. Slowly whisk in oil, then whisk in dill. Season with salt and pepper. 

Drizzle vinaigrette over asparagus and serve.