Muddle the raspberries and sugar: In a large mixing bowl, add the raspberries and caster sugar. Use the back of a spoon to press down and mash the berries until they release their deep red juice and the sugar begins to dissolve. You'll see the mixture turn a rich, ruby-red colour and smell the sweet, fruity aroma rising up.

Add the lemon juice: Pour in the freshly squeezed lemon juice and stir vigorously with your spoon. The mixture will thin out slightly, and you'll notice the sugar granules disappear as they dissolve into the tart liquid. The colour should become a vibrant, translucent pink.

Strain the syrup (optional but recommended): If you prefer a smooth drink, pour the raspberry-lemon mixture through a fine-mesh sieve into a clean jug, pressing down on the solids to extract every last drop of syrup. Discard the seeds and pulp. If you like a bit of texture, skip this step—the seeds add a pleasant crunch.

Chill the syrup: Place the syrup in the fridge for at least 10 minutes, or up to 3 days if you're planning ahead. A cold syrup ensures your drink stays fizzy when you add the sparkling water.

Assemble the drinks: Fill four tall glasses halfway with ice cubes. Divide the chilled syrup evenly among the glasses—about 3 to 4 tablespoons per glass. You'll hear the ice crackle slightly as the cold syrup hits it.

Top with sparkling water: Pour the chilled sparkling water into each glass, filling to the top. Stir gently with a long spoon; you'll see bubbles race upward and the colour lighten to a soft rose hue. The fizzing sound is your cue that it's ready.

Garnish and serve: Drop a lemon slice, a few fresh raspberries, and a mint sprig into each glass. Serve immediately while the bubbles are lively and the drink is ice-cold.