Method
Chill a Champagne flute or coupe in the freezer for 10 minutes, or fill it with ice water while you mix.
Pour 30 ml gin, 15 ml fresh lemon juice and 15 ml simple syrup into a cocktail shaker.
Fill the shaker with ice and shake hard for 10-12 seconds, until the outside of the shaker feels frosty.
Empty the glass, then strain the mixture into it through a fine strainer to catch pulp and ice chips.
Slowly top with 60-90 ml cold Champagne or sparkling wine, pouring down the side of the glass so it doesn't foam over.
Twist a strip of lemon peel over the drink to release its oils, add it to the glass and serve straight away.