Heat up the oil and when it is hot, add the celery and onion. A minute or so later, add the pancetta and fry for a few minutes. Then add the garlic. When the onion and celery have softened, add the rice and turn up the heat.
The rice should fry and go a bit translucent now, but if it starts to burn then turn it down. After a short while, add the wine or vermouth and stir while the alcohol burns off.
Turn the heat back down and when the wine has been absorbed, start adding stock a ladle at a time, stirring until it has been absorbed until it has been absorbed and then adding some more. We used some home made chicken stock for this and it does make quite a difference.
All this stirring brings out the stickiness from the rice. If you run out of stock before the rice is cooked, then just start adding water. When the rice is cooked but still has just a little bite left to it, it is done.
Shortly before it is actually done, stir in the chopped sage leaves. When it is actually done, stir in the grated parmesan and the peas and check for seaoning.