Heat the Chicken Stock, and check for seasoning.
Melt two-thirds of the butter in a large heavy-bottomed pan, and gently fry the onion for about 20 minutes and light brown. Add the rice and stir to coat, this takes only a minute.
Increase the heat, pour in 175 ml (6 fl oz) of the wine, and let it reduce to a syrup. Add the hot stock, ladle by ladle, stirring all the time, only a