Preheat oven to 350 degrees. Cream butter, add sugar. Beat together till light and creamy. Beat in egg.
Sift together flours, baking soda, salt and spices (can substitute pumpkin pie spice for mace).
Mash bananas well and combine and yogurt, stirring just till mixed. Stir in vanilla.
To butter and sugar, add dry ingredients alternately with banana mixture, beginning and ending with flour. Mix just enough to combine well.
Stir in pecans and dates. Bake in greased and floured 9x5 loaf pan 50-60 minutes. Cool in pan 5-10 minutes; then cool on rack.
Originally got this recipe from Nancy Phelps' copy of a _New York Times_ "health food" book.