In a small saucepan combine the sugar and water and heat gently over medium heat, stirring just until the sugar fully dissolves. Do not allow the mixture to boil — aggressive heat flattens aromatics and creates a cooked sugar taste. Remove from heat, add the rosemary sprig and a pinch of fine sea salt, then cover and let steep for about 5–6 minutes. This short infusion builds herbal complexity without pushing piney bitterness. Remove and discard the rosemary and allow the syrup to cool completely before using.

In a large pitcher combine the freshly squeezed blood orange juice with about 60 ml of the cooled rosemary syrup. Stir gently until fully integrated. Taste carefully — the base should feel bright, juicy, and slightly bittersweet rather than overtly sweet. If needed, add more syrup in small increments. This is the structural moment where balance is set before dilution.

Fill the pitcher generously with ice. Pour in the chilled club soda slowly to preserve bubbles, then stir once or twice only — just enough to combine. Over-stirring destroys carbonation and softens the drink’s crisp finish. The liquid should look lightly aerated and vibrant.

Pour into ice-filled glasses and garnish with blood orange slices, twists of peel, and a small rosemary sprig if desired. Serve straight away while cold, sparkling, and aromatic.