1/4 oz of creme de cassis (or blackcurrant-flavored liqueur)
2 oz of soda
1 twist of lemon
1 3/4 oz of dubonnet french vermouth (or sweet vermouth)
Stir dubonnet and creme de cassis over ice cubes in an aperitif glass. Fill with soda, add a twist of lemon peel, and serve.