Preheat oven to 180℃
Grease a loaf pan with butter and line it with baking paper.
In a medium bowl mix flour, baking soda and chai powder. Set aside.
Chop nuts and chocolate into small pieces. Set aside.
Peel the bananas, weigh and mash them with a potato masher or the back of a fork until they become a puree. Set aside.
Cream butter, oil and sugar until pale or fluffy. Add banana puree and mix until combined.
Add eggs, one at a time and whisk.
Gradually add the dry ingredients into the wet mixture. Whisk until all is incorporated. Be careful not to over mix the batter.
Add sour cream and whisk until it is well incorporated.
Add the nuts and use a spatula to fold. Then fold in the chocolate.
Transfer the batter into the prepared pan.
Bake for 55 minutes, after 30 open the oven and cover the pan with a foil (to prevent it from getting too dark).
Take out the bread from the oven and let it cool on a wire rack.
Serve with coffee and good quality butter (optional).