Pour olive oil into a 5- to 6-quart pan over medium-high heat; when hot, add onion and stir often until limp, about 5 minutes. Add rice and stir until opaque, about 3 minutes.
Add wine and stir until absorbed, 1 to 2 minutes. Add 5 1/2 cups broth, about a cup at a time, stirring after each addition until almost absorbed, 25 to 30 minutes total; stir in peas with the second cup of broth. If risotto is thicker than desired, stir in a little more broth. Stir in cheese and add salt and pepper to taste.