In a medium saucepan, bring 4 cups of water to a boil. Once boiling, remove from heat and add the dried hibiscus flowers. Let steep for about 15-20 minutes.

Strain the hibiscus tea through a fine mesh sieve into a large pitcher, discarding the flowers.

While the tea is still warm, stir in the granulated sugar until fully dissolved. Allow the mixture to cool to room temperature.

Once cooled, add the fresh lemon juice to the hibiscus tea and mix well.

In a blender, combine the hibiscus lemonade mixture with 1 cup of ice cubes. Blend until smooth and slushy.

Taste and adjust sweetness if necessary by adding more sugar or lemon juice.

Pour into glasses and garnish with lemon slices and fresh mint if desired.