Melt 2 tablespoons butter in a medium saucepan over medium-high heat. Add couscous and cook until partially toasted, 2 minutes. Add wine and cook, stirring, until almost evaporated, 2 minutes. Meanwhile, heat broth in a second saucepan until warm.
Add 1 cup broth to couscous and quickly simmer over medium-high heat until the couscous is silky and the liquid has nearly evaporated, about 3 minutes. Repeat with the remaining 2 ½ cups broth, adding a cup at a time and cooking until each addition has nearly evaporated. Before the last addition, add asparagus to remaining hot broth (about 1 ½ cups). (Stir asparagus into couscous with last cup of broth.)
Once couscous is tender and all the broth has been added, stir in Pecorino, pistachios, chervil and remaining butter. Sprinkle servings with additional Pecorino, pistachios and chervil, if desired. Serve immediately.
