- Using a mortar and pestle, coarsely crush the peppercorns. Set aside in a bowl with the lime zest and basil leaves.
- In a small pot, bring the water and sugar to a boil. Pour into the bowl of aromatics. Let cool. Cover and refrigerate for 8 hours.
- Strain the syrup and pour into a glass jar. Add the lime juice. The syrup will keep for 1 week in an airtight jar in the refrigerator.
- Divide the cold syrup and beer among four lowball whisky glasses. Garnish with the lime slices and basil leaves.