1. Make the sorrel: In a medium saucepan, combine the hibiscus flowers, sugar, cinnamon stick, cloves and ginger. In a small pot set over high heat, bring 6 cups water to boil. Pour the boiling water over the dry ingredients and give them a stir. Let cool to room temperature. Once cool, cover, place in refrigerator and let steep for two days. Strain through a fine-mesh sieve and store the liquid in a lidded container in the refrigerator.

2. Make the lemonade: In a large container, combine 2 cups water, the lemon juice and the simple syrup.

3. Make the cocktail: In a Collins glass filled with ice, add the lemonade and the rum. Top with the sorrel. Garnish with the mint sprig and serve.