In large bowl, mix flour, baking powder and salt. Cut in shortening until mixture resembles peas. Add orange and lemon peels, sweet potatoes and agave and mix well. Add enough milk to make soft, but not sticky, dough. Turn out onto floured board and knead 3 to 4 times. Pat to 1-inch thickness and cut out 2-1/4-inch rounds. Place on ungreased cookie sheet and bake at 400°F for 15 to 18 minutes or until lightly browned.