Scrape the seeds out of the vanilla pod and mash them with a little of the sugar so they separate.
Put the frozen strawberries, sugar, water, vanilla seeds and the empty vanilla pod in a saucepan and bring to the boil.
Turn down to medium heat and let the compote simmer for about 5-6 minutes, - or until the berries are just tender.*If using fresh strawberries, the cooking time is shorter.
Stir the cornflour into a couple of tablespoons of cold water and pour it into the compote, stirring as you go. Let the compote cook for a further 5 minutes or so over medium heat, - or until the berries are completely tender.
Take the pan off the heat (remove the vanilla pod first) and blend the compote lightly with a stick blender.*You can skip this step if you prefer the compote with lots of whole berries, - at home we prefer it lightly puréed.
Cut the fresh strawberries into small dice and stir them into the hot compote.*The fresh strawberries give the compote a lovely freshness and a really pleasant texture, as they are barely heated through.
Put the compote in the fridge and let it chill completely before serving.