In a medium saucepan, combine the raspberries, the zest and juice of both oranges, and the juice of the lemon. Use a spoon or potato masher to gently crush the raspberries and release their juice.

Add the water to the saucepan and bring everything to a gentle simmer over medium heat. Stir occasionally, making sure the raspberries break down and release their colour. Let it simmer for about 15 minutes.

Once the fruit has softened, strain the mixture through a fine sieve or cheesecloth into a clean bowl, pressing down on the fruit to extract all the juice. You can discard the pulp or save it for smoothies or baking.

Pour the strained liquid back into the saucepan and add the caster sugar. Stir until the sugar is completely dissolved. Bring the mixture to a simmer again and cook for another 10-15 minutes, allowing it to reduce slightly and thicken into a syrup.

Once the cordial has thickened and reached your desired sweetness, remove from the heat. Allow it to cool, then transfer to a clean bottle or jar. Store in the fridge for up to 2 weeks.