Add the cream, sugar and scraped vanilla into a heavy base pot and bring to the boil.
In a separate container add cold water and place the gelatin into the water and allow to bloom.
Once the cream, sugar, vanilla has come to the boil, squeeze out the gelatin and add it to the now hot liquid, then add in the buttermilk to the mix.
Skim the top of the mix and take away any heavy bubbles. Pour into a ramekin and place into the fridge and allow to set.
Add the gelatin into the water one by one, if you put the two in at the same time the water doesn't cover the surface of the gelatin and it won't bloom properly.
Do not add the buttermilk to the cream at the start - it may appear you are saving time but the buttermilk will split and the whole dish will be ruined.
Why not add some fruit to the panna cotta - it will work great with strawberries or blackberries depending on the season.