Place the first 4 ingredients in a blender and blend until smooth. Add the buttermilk and blend again.
In a large bowl, sift together the flour, baking powder, baking soda, nutmeg and salt. Add sugar. Stir in the nuts. Add the banana mixture to the flour mixture and stir until combined. Batter will be slightly lumpy.
Pour batter into loaf pan and bake 55 minutes or until a knife inserted comes out clean. Let bread cool and cut into slices.