2 to 3 medium overripe bananas  peeled (about 1 1/4 to 1 1/2 cups mashed) 1/3 cup butter, unsalted or salted, melted 1/2 teaspoon baking soda (not baking powder) 1 pinch salt 3/4 cup sugar (1/2 cup if you would like it less sweet, 1 …