Prepare the peas:
1. Heat the butter in a saucepan over medium heat, add the onion and celery, stirring from time to time for 3-4 minutes until the onion is soft but not browned.
2. Add the peas, the half-liter of broth, the bouquet garni and cook over a low flame for 15-20 minutes. Season with salt and pepper to taste.
For the risotto:
3. Heat the olive oil in a saucepan, lightly fry the onion for 3-5 minutes over medium heat, add the rice and stir to coat, add a ladleful of broth and continue cooking by adding the boiling broth a ladle at a time, stirring continuously.
4. Towards the end of the cooking time add the peas and their cooking liquid. Stir until the risotto is cooked. Adjust salt and pepper to taste.
5. Finally add more broth until the risotto is almost, but not quite, as liquid as a soup.
6. Serve immediately with the parmigiano separately on the side.