Melt the butter with the oil in a saucepan, add the onion and garlic and cook until the onion is soft and starting to brown. Add the rice and stir until coated with the butter mixture.
Add the hot stock, a ladleful at a time, and cook, stirring constantly, until each addition has been absorbed before adding the next. Continue until all the stock has been absorbed and the rice is creamy and cooked but still retains a little bite – this will take around 15 minutes.
Add the peas and heat through for 3–5 minutes. Remove from the heat and stir in the Parmesan, ham and parsley. Season to taste with salt and pepper and serve immediately.