6 cups vegetable stock, preferably homemade
1/4 cup olive oil
1 small onion, finely chopped
1 cup Arborio or Carnaroli rice
1/2 cup dry white wine
1 bunch asparagus, trimmed, stalks cut into 2-inch lengths
1 cup thawed frozen peas
1 teaspoon grated lemon zest, plus more for garnish
2 tablespoons fresh lemon juice
1 cup chopped fresh flat-leaf parsley leaves
1/2 cup finely grated Parmigiano-Reggiano, plus more for serving
Coarse salt and freshly ground pepper
Bring stock to a simmer in a medium saucepan.
Heat 2 tablespoons oil over medium heat in another saucepan. Cook onion, stirring frequently, until soft, 6 to 7 minutes. Add rice, cook, stirring, until edges are translucent, 2 to 3 minutes. Add wine; cook, stirring, just until evaporated.
Add 1/2 cup hot stock; cook, stirring, until almost absorbed. Continue adding 1/2 cup stock in this manner until liquid is creamy and rice is al dente, about 20 minutes total (you may not need to add all the stock). Add asparagus with the last addition of stock, and the peas about 1 minute before risotto is done.
Remove from heat; stir in lemon zest and juice, parsley, cheese, and remaining 2 tablespoons oil. Season with salt and pepper. Serve immediately with additional cheese and lemon zest.