In a heavy bottom pan melt the butter and add the onions. Cook for about 3 minutes and add the bacon. Cook until the onions are translucent and the bacon is starting to crisp up. Add a 1/3 cup of champagne to the pan and let it cook for a minute. Add the rice, stir well until all the liquid is absorbed by the rice. Add the remaining champagne, stirring and insuring it will not overspill as it may do to the effervescence of the champagne. Lower the heat, semi-cover with a lid and simmer for 15 minutes. Stir occasionally and add chicken stock if becomes too dry. Season with salt and pepper. Cook another 10 to 15 minutes or until the rice is cooked to desired doneness.