extra-virgin olive oil, divided • small yellow onion, finely chopped (about 1 cup) • medium garlic cloves, thinly sliced • arborio or carnaroli rice • dry white wine • kosher salt • chicken or vegetable broth, preferably homemade • fresh or frozen peas • freshly grated parmesan cheese, plus more (optional) for serving • unsalted butter (optional) • Chopped fresh flat-leaf parsley, for garnish