1/2 oz. fresh lime juice
1/2 oz. demerara syrup
2 oz. rum (see Note)
Garnish: None
Add the ingredients to a cocktail shaker filled with cracked or cubed ice. Shake and strain into an ice filled old-fashioned glass.
Note:
If you want to truly mimic a grog from the 1700s, use a pot still unaged rum or a black pot still rum. (And skip the ice. And the clean glass. And maybe add some brackish water. Maybe not). If your looking for a nineteenth-century-style grog, try a black blended rum. For a more refined grog, choose a blended aged rum.