1
Melt and cool the butter.
2
Mix dry ingredients in a large bowl.
3
Roughly mash 2 of the bananas so some texture remains.
4
Combine the remaining 2 bananas and the brown sugar using the wire whisk attachments on an electric mixer. (Do it like you mean it; at least 3 minutes.)
4
Whisk in the eggs, butter, and vanilla, just until incorporated.
5
Fold in the chunky bananas and walnuts.
6
Spoon into prepared (lightly buttered or lined with cups) muffin tins (small sized).
7
Bake for 18-20 minutes, turning halfway through.
8
Let cool for a few minutes, then turn onto a board or rack to finish cooling.