Blend until combined but still retaining some texture – it needs to be sticky enough to be able to easily stick together. However, be careful not to over-blend, as the mixture will become very greasy as the oils will be released from the nuts.
Transfer the mixture to a loaf tin lined with greaseproof baking paper (I used a one-pound loaf tin).
Smooth over the top.
Decorate with goji berries and chopped pistachios, if desired.
Place in the fridge for at least 30 minutes for it to firm up before cutting.
Remove from the loaf tin and cut into pieces.
Keeps covered in the fridge for a good few days.
For a nut-free version, use sunflower seeds instead of walnuts, and use tahini instead of almond butter.