Combine the cashews with the water and leave to soak overnight.
Preheat the oven to 400 F/ 200 C/ gas mark 6. Line a muffin pan with 8 muffin cases. Set aside.
Combine the flour with the baking powder and stir thoroughly.
Puree the cashews (as well as the water) with the avocado and lime juice.
In a large bowl beat the egg, sugar and oil until smooth and a little lighter in colour. Add the vanilla extract, lime zest and the avocado mixture. Stir thoroughly.
Add the raspberries and flour mixture and stir only until the flour is no longer visible. Spoon the mixture into the muffin cases, sprinkle each muffin with a little demerara sugar and bake for 36 minutes. Remove from the pan and place on a cooling rack. Yields 8 large muffins.
Preparation time does not include time needed to soak the cashews.