Black Walnut Banana Muffins

3 bananas
1/2 cup granulated sugar
1/2 cup packed brown sugar
2 eggs
1/2 cup butter or margarine, melted
1 cup all-purpose flour
1 cup wheat flour
1 1/2 teaspoons baking soda
3 tablespoons buttermilk
2/3 cup black walnuts, chopped

Heat oven to 300 degrees F.

Mash bananas in a medium bowl. Add sugar, brown sugar, and eggs; mix well. Add margarine. Stir in flour and baking soda. Add buttermilk and black walnuts. Mix until just moistened. Spoon into paper-lined muffin tins. Bake for 20 minutes.