Turn the oven on to 350°F. Spray a 9-by-5-inch loaf pan with cooking spray very lightly. Make holes all over the sweet potato with a fork and transfer to a medium microwave-safe dish.
For 8 to 10 minutes, on High, with a single rotation, microwave the potato until the skin starts to wrinkle and a fork or paring knife can easily pierce it through all the way to the core.
Allow it stand at room temperature for approximately ten minutes, or until manageable.
Meanwhile, in a medium basin, thoroughly mix together all-purpose flour, whole-wheat flour, baking powder, cinnamon, baking soda, allspice, nutmeg, and salt.
Cut the sweet potato open lengthwise when it has partially cooled. Remove the meat with a spoon and place it in a large mixing bowl; throw away the skin.
Mash with a fork for about 45 seconds, or until there are no big clumps remaining (you should have around 1 cup). Whisk in the eggs, milk, oil, vanilla, and maple syrup until smooth.
Pour the batter into the loaf pan that has been ready. Bake for 40 to 45 minutes, or until golden brown and a wooden pick inserted in the center comes out clean.
Let cool for half an hour in the pan on a wire rack. After removing from the pan, let it cool fully on the rack for thirty to sixty minutes.