For the Black Pepper Date Simple Syrup, place all ingredients, except cornflour, in a medium saucepan, bring to a simmer stirring to dissolve sugar. Strain mixture through a fine mesh sieve, being careful not to press too much of the pulp solids through the strainer. Place cornflour in small bowl. Add 2 tablespoons of the strained date mixture with the cornflour; mix well.
Return remaining strained date mixture to the saucepan. Stir in cornflour mixture with whisk until well blended. Bring to a simmer and cook stirring for a 1 minute. Remove from heat. Cool slightly. Store syrup in tightly covered, clean container in refrigerator until ready to use. (Makes 1 ½ cups syrup. Enough for 12 Black Pepper Date Cocktails.)
For 1 Black Pepper Date Cocktail, place ice in cocktail shaker. Add Black Pepper Date Simple Syrup, rum, elderflower liqueur and lime juice; shake until well mixed and chilled. Strain into beverage glass. Garnish with a sprig of fresh rosemary, if desired. Serve immediately.
Leftover Black Pepper Date Simple Syrup can be used to prepare additional Black Pepper Date Cocktails or other cocktails using caramel-coloured distilled spirits, such as rum, bourbon, whiskey and scotch.