Make the simple syrup: In a small saucepan, combine the 150g caster sugar and 150ml water. Place over a medium heat and stir gently until the sugar has completely dissolved – you'll see the liquid go from cloudy to perfectly clear, with no gritty grains remaining. This takes about 3-4 minutes. Once clear, remove from the heat.

Infuse the berry flavour: Add the 125g raspberries to the hot simple syrup. Use a fork or a muddler to gently crush the berries into the syrup. You'll see the syrup turn a deep, vibrant pink almost instantly, and the kitchen will smell wonderfully fruity. Let this mixture steep for 5 minutes to allow the flavours to really meld.

Strain the berry syrup: Pour the berry-syrup mixture through a fine-mesh sieve set over a heatproof bowl or jug. Use the back of a spoon to press down on the berry pulp to extract every last drop of pink syrup. Discard the seeds and pulp left in the sieve. You should be left with a beautifully clear, jewel-toned syrup.

Juice the lemons: While the syrup cools slightly, roll your lemons firmly on the countertop to help release the juices. Cut them in half and juice them until you have about 250ml of fresh lemon juice. Strain the juice through a sieve to catch any pips and pulp, giving you a smooth base.

Combine the base: In a large serving jug or pitcher, pour in the cooled pink simple syrup and the fresh lemon juice. Stir them together until they are completely combined. You'll have a concentrated, deeply pink and intensely flavoured lemonade base. At this stage, taste it – it should be very sweet and very tart. You can pop this base in the fridge to chill for at least 30 minutes, or up to 2 days.

Add the fizz and serve: Just before you're ready to serve, take your chilled lemonade base and add the 1 litre of chilled sparkling water. Stir gently but thoroughly. You'll see the mixture lighten in colour and become wonderfully effervescent, with tiny bubbles racing to the surface. Fill glasses with ice cubes, pour the sparkling pink lemonade over the top, and garnish with a lemon slice, a few fresh berries, and a sprig of mint if you like. Serve immediately.