In a small bowl, place 2 tablespoons of the skimmed milk and sprinkle the gelatine on top. Leave to soak for about 10 minutes.
Meanwhile heat the remaining milk, with the split vanilla pod and sugar on a medium heat until the sugar is fully dissolved.
Remove from the heat and stir through the gelatine, then mix through the yoghurt.
Lightly brush a ramekin with olive oil and place the yoghurt mixture inside.
Cover and refrigerate for at least 2 hours.
For the coulis, place the blackberries in a pan on a low heat with a tablespoon of water. Heat slowly until the fruit has fully softened, adding more water if needed. Add a little bit of icing sugar to give a shiny gloss to the coulis and pass it through a sieve.
To serve, dip the ramekin three-quarters of the way in warm water and invert onto a plate. Pour the coulis around the panna cotta, decorate with a blackberry and serve.