Fill a cocktail shaker with ice. Pour in the gin, lemon juice and simple syrup (or sugar cube). Shake vigorously  until well chilled, about 30 seconds. Strain the liquid into a champagne glass and top with Champagne.

Take a lemon slice and cut off the lemon rind so that you have one long continuous strip of lemon peel. Twist your lemon peel into a tight curl and hold it for a few seconds to retain the shape. Garnish your glass with the lemon twist.