1. Heat water and sugar over low heat in a medium saucepan, stirring until the sugar is dissolved. Remove from heat and add the elderflowers. Cover and let steep for at least 4 hours, but preferably overnight.
2. Strain the mixture through a fine mesh strainer, pressing the flowers with the back of a soup spoon to extract as much flavor from them as possible. Add the lemon juice and white wine. Chill the mixture thoroughly, then freeze in your ice cream maker according to the manufacturer’s instructions.