Add the water and the sugar to a pan and gently bring to the boil. It must reach soft-ball texture, so it looks like a clear syrup. Whisk the egg yolks and trickle in the sugar solution a little at a time – you can use a Kenwood for this – until the mix is full of volume. Allow this mix to cool for about 10 minutes.
In a clean bowl, semi-whip the cream until it reaches ribbon stage. Then gently fold it into the egg yolk and sugar mix, using a cutting/folding action.
Add the whisky to taste, then the toasted pinhead oats and combine. Pour into a terrine mould double-lined with cling film and freeze overnight.
To serve remove from the freezer, tip the parfait out of the mould and remove cling film. Then cut into slices and place on cool plates and serve with a few berries, some sweet cicely and some of those buttery sugary oats. Now eat!