Step 1: Combine 250g of raspberies, 50g of caster sugar and 100ml of water in a saucepan. Step 2: Bring to the boil, then simmer for 5 minutes until the fruit is soft. Stir in one teaspoon of vanilla extract and leave to cool slightly. Step 3: Purree the mixture for one minute until smooth. Step 4: Strain through a sieve, using the back of a spoon or ladle to push through as much liquid as possible.