2 1/2 oz gin
1 1/2 oz lemon juice
1 tsp superfine sugar
4 oz club soda
1/2 oz creme de cassis

In a shaker half-filled with ice cubes, combine the gin, lemon juice, and sugar. Shake well. Strain into a collins glass almost filled with ice cubes. Add the club soda. Stir well. Drop the cassis into the center of the drink.