Preheat oven to 350°F (175°C).

Prepare muffin pans with paper liners (optional).

In a large bowl, mash the ripe bananas using a potato masher.

Add whisked egg, melted butter, whole milk, vanilla extract, and brown sugar to the mashed bananas.

In a separate small bowl, sift together the flour, baking soda, cinnamon, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing gently until just combined. Be careful not to overmix.

Fold in the sweetened shredded coconut and chopped walnuts.

Fill each muffin liner about 2/3 full with the batter.

Sprinkle the muffin tops with reserved walnuts, crushed banana chips, and brown sugar.

Bake for 15-20 minutes, or until a toothpick inserted into the center comes out clean.

Let the muffins cool in the pan for a few minutes before transferring them to a wire rack to cool completely.

Serve with hot Japanese herbal tea (optional).