Measure and sieve the sathu maavu flour, whole wheat flour, baking soda, baking powder, and salt. Also, preheat the oven to 180 degrees for 10 minutes.
Take a ripe banana, add in sugar and mash it well with a fork. Alternatively, you can blend the chopped banana pieces in a blender to puree them.
Once the bananas are well mashed, add oil and vanilla essence.
Stir it well with a hand whisk until the oil is mixed evenly. Now add the sieved whole wheat flour and sathu maavu flour mixture to the wet ingredients.
Gently fold everything well for 10-15 seconds. Don't over mix. The final mixture should be thick. Add in broken walnuts at this stage. Give a quick stir.
Line up the muffin tray with muffin liners. Pour the prepared batter into muffin liners and top it with broken walnuts. Bake in the preheated oven for 20- 25 minutes (baking time depends on the size of the muffin tray and oven) at 180° Celsius till a toothpick inserted in the center comes out clean. Allow cooling in the tray for 5 minutes once done.