Heat oven to 350F. Lightly grease a 9x5 loaf pan. Line with parchment paper and grease and lightly flour it.

In a large bowl mash the bananas.

Add butter, yogurt, brown sugar, eggs and vanilla. Combine well.

In a medium bowl mix both flours, baking soda a salt. Add to banana mix and combine using a spatula.

Gently add the chocolate and walnuts, and mix until incorporated.

Pour batter into loaf pan and spread into an even later. Sprinkle the surface with the coarse sugar.

Bake for 75 minutes until edges of loaf start to pull away from the pan. Transfer to cooling rack and run a thin knife around the edge of the banana bread to separate it from the pan.

After 15 minutes of cooling, unmold and cool completely.