1/2 cup melted unsalted butter, more for greasing tins

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The Minimalist: Whole Wheat Muffin, the Remix (February 10, 2010)

2 1/2 cups whole wheat flour, preferably pastry flour

3/4 to 1 cup sugar, depending on sweetness of fruit

2 teaspoons baking powder

1/4 teaspoon baking soda

1/4 teaspoon salt

1 cup mashed or puréed banana, sweet potato, apple, zucchini, cooked or canned pumpkin, or other fruits or vegetables

1 egg, beaten

1/2 cup buttermilk.