Prick a large sweet potato all over and roast at 400F for 50 to 60 minutes, until collapsing and a knife meets no resistance.

Split it, scoop the flesh, mash it smooth, and cool to room temperature. Measure out 1 cup.

Whisk the flour, cinnamon, nutmeg, baking soda, baking powder, and salt together in a large bowl.

In a second bowl, whisk the mashed sweet potato with the brown sugar and maple syrup until smooth, then whisk in the oil, eggs, milk, and vanilla until no orange streaks remain.

Pour the wet into the dry and fold about 12 strokes, stopping while streaks of flour and small lumps are still visible. Fold in the pecans on the last stroke or two.

Let the batter rest 15 minutes while the oven heats to 425F.

Line 12 muffin cups and fill each nearly to the rim.

Bake at 425F for 5 minutes, then lower the oven to 350F without opening the door and bake another 15 to 17 minutes.

They are done when the tops spring back and a toothpick comes out with a few moist crumbs.

Cool 5 minutes in the tin, then transfer to a rack.