01 - In a small saucepan, combine the honey, lemon juice, water, raspberries or strawberries, and sugar if using. Gently mash the berries with a muddler or fork. Heat over low heat for 2 to 3 minutes, stirring continuously, until the honey fully dissolves and the mixture takes on a vibrant pink color.
02 - Pour the warm syrup through a fine-mesh sieve into a bowl or jug. Press firmly on the fruit solids to extract maximum color and flavor. Discard the solids and set the syrup aside to cool slightly.
03 - Fill four serving glasses generously with ice cubes. Divide the pink honey-lemon syrup equally among the glasses, pouring about 3 tablespoons of syrup into each.
04 - Pour chilled sparkling water or club soda over the syrup in each glass, dividing the full 3 cups evenly. Stir gently to combine without losing the carbonation.
05 - Finish each glass with a lemon slice and a sprig of fresh mint. Serve immediately while the soda is cold and effervescent.