Warm the stock in a small saucepan and keep over low heat.
In a wide pan, heat the olive oil (or butter) and sauté the onion until soft and translucent.
Add the rice and stir until each grain is coated and lightly toasted.
Pour in the white wine and cook until absorbed.
Begin adding the stock one ladle at a time, stirring constantly and waiting until absorbed before adding more. Continue until the rice is creamy and tender, about 18–20 minutes.
Stir in the lemon zest, Parmigiano, and a final swirl of butter or olive oil. Adjust seasoning with salt.
Garnish with parsley and serve hot.