Grease and flour a 9x5" loaf pan. Preheat oven to 350~. Mix together flour, baking powder, baking soda and salt. In large bowl beat butter and sugar until light and fluffy. Mix in eggs, milk, orange juice and grated orange peel. Stir until blended. Gradually stir in flour mixture until blended. Fold in blueberries and walnuts. Spoon batter into pan. Remove from oven and cool. Wrap in aluminum foil and store overnight in refrigerator before slicing. ----