Brew the hibiscus tea: In a medium saucepan, bring 2 cups of water to a boil. Add the dried hibiscus flowers, reduce heat to low, and simmer for 5 minutes. The liquid should turn a deep red color as the flowers release their flavor and color.
Strain and sweeten the tea: Remove from heat and strain the liquid through a fine-mesh sieve into a heat-safe container, pressing on the flowers to extract maximum flavor. Immediately stir in the sugar or honey while the liquid is still hot so it dissolves completely.
Cool the hibiscus concentrate: Allow the hibiscus tea to cool to room temperature, then refrigerate for at least 10 minutes until chilled. This step is crucial as we don’t want to melt all the ice in the blender.
Prepare the lemon juice: While the tea is cooling, juice your lemons to get ¾ cup of fresh juice. Make sure to strain out any seeds. If using, zest one lemon before juicing to get your tablespoon of zest.
Blend everything together: In a blender, combine the chilled hibiscus tea, fresh lemon juice, lemon zest, and ice cubes. If using vanilla extract, add it now. Blend on high speed until smooth and slushy. The consistency should be similar to a frozen margarita.
Taste and adjust: Pause to taste your concoction. Add more sugar or lemon juice if needed, blending briefly after each addition until you reach your desired balance of sweet and tart.
Serve immediately: Pour into chilled glasses and garnish with fresh lemon slices and mint leaves. For the best experience, serve with both a straw and a spoon – the drink will be slushy and perfect for a hot day!