01 - Bring 4 cups of water to a rolling boil in a medium saucepan over high heat.
02 - Remove saucepan from heat and immediately stir in the dried hibiscus flowers. Cover and let steep for 10 minutes to extract full flavor and deep red color.
03 - Pour the mixture through a fine-mesh strainer into a heatproof pitcher. Discard the spent hibiscus flowers.
04 - While the tea is still warm, add the granulated sugar and optional honey or agave syrup. Stir continuously until completely dissolved.
05 - Allow the tea to cool to room temperature, then refrigerate for at least 1 hour until thoroughly chilled.
06 - Fill serving glasses with ice cubes and fresh lime slices. Pour the chilled hibiscus tea over the ice. Garnish with fresh mint leaves if desired and serve immediately.