Gently boil the double cream until most of the water has evaporated and the cream begins to change colour.
Add the butter and continue to boil, stirring frequently. It will look as though it has curdled, but don't worry - this is normal!
When the butter begins to change remove from the heat and transfer to a heatproof bowl to cool.
Whilst the butter is cooling, add the miso, water and lecithin to a blender and blend until smooth. With the blender still running, slowly pour the oil into the mixture.
When the butter has cooled, slowly add the butter mixture to the running blender, ensuring all solids are transferred across too.
You can now transfer the mixture to a freezer for long term storage or whip it with a hand mixer to produce a fluffy pale mixture - which can be used straight away or stored in a fridge for a few weeks.