Pour the ProZero into a small saucepan.
Add the butter, sugar and cornflour.
If you are using a vanilla pod, cut it in half lengthwise and remove the tiny seeds from the inside with a sharp knife. Place the seeds and the cut vanilla pod into the small saucepan. If you are using vanilla essence instead, add this to the pan.
Place the pan over a gentle heat and stir well.
Keep stirring until the mixture starts to simmer and is thickened.
Take out the cut vanilla pod.
Pour the Panna Cotta mixture into a tall container or jug and use an electric hand-held blender to blend for 30-40 seconds.
Immediately pour the mixture into the ramekin dishes.
Leave to cool, then place into the fridge to set for 3-4 hours.
Serve with permitted fruits.
ProZero is a food for special medical purposes and must only be used under strict medical supervision.