Directions

1. Preheat oven to 350°F. Lightly coat a 9-by-5-inch loaf pan with cooking spray. Using a fork, poke holes all over sweet potato; place in a medium microwave-safe dish. Microwave on High, rotating once, until the skin begins to wrinkle and the potato is easily pierced with a fork or paring knife all the way to the center, 8 to 10 minutes. Let stand at room temperature until easy to handle, about 10 minutes.
2. Meanwhile, whisk all-purpose flour, whole-wheat flour, baking powder, cinnamon, baking soda, allspice, nutmeg and salt in a medium bowl until fully combined.
3. Cut the partially cooled sweet potato open lengthwise. Scoop out the flesh and transfer to a large mixing bowl (discard the skin). Mash with a fork until no large clumps remain, about 45 seconds (you should have about 1 cup). Add milk, maple syrup, oil, vanilla and eggs; whisk until smooth. Gradually add the flour mixture, whisking until just combined.
4. Transfer the batter to the prepared loaf pan. Bake until golden brown and a wooden pick inserted in the center comes out clean, 40 to 45 minutes. Cool in the pan on a wire rack for 30 minutes. Remove from the pan and cool completely on the rack, 30 to 60 minutes.