Combine the light brown sugar and water in a small saucepan and heat gently over medium heat, stirring continuously until the sugar fully dissolves into a smooth, glossy syrup. Do not allow the mixture to boil or reduce aggressively — overheating will concentrate sweetness and mute the subtle molasses depth that gives this mocktail its cocktail-like backbone. Remove from heat and let cool completely before using.

Add the fresh blackberries and mint leaves to a large pitcher or mixing bowl and gently muddle just until the berries release vivid purple juice and the mint becomes fragrant. The goal is controlled extraction, not purée. Overworking the fruit or tearing the mint will create cloudy texture and introduce harsh green bitterness that disrupts the drink’s clean, structured profile.

Pour in the fresh lime juice, white verjus, and about 80 ml of the cooled brown sugar syrup, then stir slowly until the liquid becomes evenly integrated and lightly aromatic. Taste the base before dilution — it should feel slightly too intense, with clear acidity, subtle sweetness, and a faint wine-like edge. This pre-balance ensures the drink remains vibrant once carbonation and ice soften the structure.

Fill the pitcher with plenty of ice and add the chilled club soda last. Stir once or twice only to combine. Excess agitation will flatten the drink and destroy the lifted, sparkling texture that defines a mojito-style mocktail. Add a small pinch of fine sea salt and give a final gentle stir to connect the fruit, citrus, and verjus into a cohesive whole.

Pour into ice-filled glasses and garnish with fresh mint sprigs, lime wedges, and a few whole blackberries. Serve while fully cold and sparkling for maximum aromatic brightness and refreshing clarity.