Citronade is currently the name given to a cocktail made from lemonade and lemon vodka. It seems likely, therefore, that what is being referred to here is citronnade (almost invariably spelt with a double 'n'), the french word for a type of lemonade made from fresh lemon juice, lemon zest, and sugar. When the pulp, juice and zest of the lemons are used, and the mixture is cooked for some time, the drink is often referred to as Tunisian citronnade.
Click here for a simple citronnade recipe (instructions in French)
Click here for the more complex Tunisian citronnade (instructions in French)