Heat the oil in a saute pan. Add the celery, parsley and some pepper and cook, stirring, over medium heat for 2-3 minutes. Add the ham and stir. Add the peas and 1/4 cup chicken stock, bring to a boil, then reduce heat and simmer, uncovered, until most of the liquid has evaporated. Set aside.

Put the remaining stock in a separate pan and bring to a simmer.

Melt the butter in a large, heavy-based saucepan. Add the onion and stir until softened. Add the rice and stir well, making sure the rice is coated with the butter. Gradually stir in the hot stock, 1/2 cup at a time. Stir until the liquid has been completely absorbed before adding more. Stir over low heat until all the stock has been absorbed and the rice is creamy and tender. (It should take 25-30 minutes.) Season to taste.

Add the pea/ham mixture and grated Parmesan and serve with Parmesan shavings and black pepper.