It's really simple to scale this one up - you just need to (roughly) follow the 3-2-1 ratio. So three parts prosecco, two parts limoncello and one part soda water. Or to make things even easier, use one bottle of prosecco, two cups of limoncello and one cup of soda. Don't add the ice to the bowl or jug with the cocktail in it because the ice will melt and dilute it. Instead, I like to pop ice in the serving glasses, and then top with the cocktail.