Preheat the oven to 180 C / Gas 4. Sift together the wholemeal flour, Splenda®, cocoa, bicarbonate of soda and salt.
In a separate bowl, add beans and 80ml (1/3 cup) water to bowl and blend. Sieve bean mixture to remove any lumps or skins. This should now be 240ml (1 cup) of bean liquid. if there is not enough, make it up to with water (this replaces the oil or butter you would normally use).
In a third bowl, whisk egg whites until stiff.
Add dry ingredients to wet, including the remaining 240ml (1 cup) water and the vanilla. Once combined, gently fold in egg whites.
Bake in the preheated oven until a skewer inserted near the centre comes out clean, about 15 minutes.
While they are baking make the frosting. Combine the plain flour, the 30g cocoa, skimmed milk and 12g Splenda®.
Microwave the frosting on high power for 3 to 5 minutes. Whisk in 120ml cold milk. Frosting can be poured over hot cupcakes straight out of the oven and allowed to set at room temperature.
Add 1/4 tsp chilli powder and cinnamon to the batter.
Don't have butterbeans, any kind of plain bean will do. Alternatively use applesauce, but this increases the sugar content.