Place the fruit into your small metal saucepan. Add the caster sugar and the fresh lemon juice. Pour in one tablespoon of water to the pan.

Set your stove to a medium heat setting. Stir the berries gently as the sugar starts melting. Let the mixture simmer for about five minutes.

Remove the pan from the heat very carefully. Use your blender to puree the softened red fruit. Blend until the mixture looks very smooth and liquid.

Set your fine sieve over a clean bowl. Pour the hot liquid through the small mesh holes. Use a spoon to push all the juice through.

Discard the seeds left inside the mesh sieve. Let the smooth sauce cool down at room temperature. It will thicken slightly as it gets colder.