To create a smooth cream, it helps to soak the cashews first. For the quick method, soak the cashews in a bowl of boiling water for at least 10 minutes. If you have the time, the optimal method is to soak the cashews in cold water for several hours or overnight.
Heat a large frying pan on medium heat then add the oats. Toast for around 5 minutes, tossing regularly. The cooking time will depend on the heat and the type of oats, but they're done once they've turned slightly brown and have a light nutty smell (just be careful not to burn them). Once toasted, set aside and allow to cool.
Set aside around half of the raspberries, then mash the other half in a bowl using a fork until you have a thick purée. If you want to keep them all whole, simply skip this step.
Once the cashews have soaked, drain them and rinse with cold water. Add these to a blender along with the measured water, whisky, and agave syrup. Blend until very smooth, which may take a minute or two. Stop to scrape down the sides, adding small amounts of extra water if necessary to help it along.
In four individual glasses or bowls, begin to spoon in layers of the oats, mashed raspberries, cream, and whole raspberries. Take ⅛ of each component at a time to end up with four glasses each with two layers (saving some oats and raspberries to finish).Note: You can also combine the oats with the cream before assembling, but I prefer to just add them in separately.
Serve immediately, or chill in the fridge for up to 24 hours before serving.