Preheat the oven to 175C (fan forced).
Place muffin liners in a standard size (12 hole) muffin tin and set aside.
Place all the dry mix ingredients into a bowl and whisk thoroughly to combine. Set aside.
In a medium size bowl, cream the butter and sugar together. You can do this with a spoon but I prefer to use a hand held mixer.
Add the eggs and mix thoroughly.
Stir in the mashed banana, vanilla and salt, ensuring it is well incorporated.
Stir in the cocoa nibs and walnuts.
Add the dry mix to the wet mix and gently fold the dry ingredients in with a spatula. Do not over-mix at this point or your muffins will be dense. You want to mix it only enough such that the dry ingredients are just incorporated.
Spoon dessertspoonfuls of the mixture into the prepared muffin pans.
Bake for 20 minutes until they are well risen and golden brown.
Remove the muffin tin from the oven and allow to sit for five minutes.
Remove the muffins from the tin and place onto a rack.
Allow to cool completely.
Store at room temperature for two days or freeze immediately for up to three months.