Preheat the oen to 180 C (350 F). Take a roughly 10-inch square of baking paper, crumple it up then un-crumple and use it to line an 8-inch square cake tin.
Cream together the nut butter, eggs, sugar and vitafiber in a bowl until smooth. Add the vanilla, salt, baking powder and desiccated coconut. Stir together well. Scrape into the lined pan and smooth out in an even layer. Dot with the chunks of chocolate then sprinkle with a touch of Maldon salt and some coconut flakes.
Bake for 20-25 minutes. It won't look like it has browned much but, when poked, the middle should feel at bit squidgy and the edges should feel firm. Leave to cool before slicing into 16 squares.