For raspberry simple syrup, combine sugar and water in a small saucepan. Cook over medium heat for 2 to 4 minutes or until mixture thickens and is syrup-like, stirring frequently. Remove from heat. Stir in raspberries; slightly mash with the back of a spoon. Cool completely.

Strain raspberry mixture through a fine-mesh sieve set over a bowl, pressing with back of a spoon. Discard pulp. Store syrup covered in refrigerator up to 5 days.

For cocktail, add bourbon, grapefruit juice and raspberry simple syrup to an ice-filled cocktail shaker. Cover and shake well until chilled. Strain into 2 (6-oz.) martini glasses. Garnish with raspberries and grapefruit quarters threaded onto cocktail picks, if desired.