Saute the onion gently in half the butter until soft. Add the rice and turn the grains over in the butter and onion until coated and shiny. Add the wine and stir thoroughly. After 1 minute, add the first ladleful of hot stock. Stir and allow the liquid to cook away, then add the next ladlefu. Wait for the grains to absorb the stock, stirring gently, then add more stock. Continue this way for about 20 minutes until the rice is soft, tender and creamy but the grains must remain firm in the center. Season with salt and pepper and remove from the heat. Stir in the rest of the butter, parsley and cheese. Stir thoroughly and cover. Leave the risotto to rest for 2 minutes, then transfer to a warmed platter and serve at once.