In a large bowl, whisk together flour, baking powder, baking soda, salt, and all the spices.

In a medium bowl, whisk together brown sugar, maple syrup, vegetable oil, pumpkin purèe, eggs, and buttermilk until well combined.

Pour wet mixture into the flour mixture and gently fold together until just combined. Do not over mix.

Cover bowl and let sit at room temperature for 15 - 30 minutes to one hour.*

Preheat the oven to 425 degrees F and line a 12 cup muffin pan with muffin liners.

In a small bowl, mix the turbinado sugar with the cinnamon, if using. Set aside.

Divide the batter evenly between the muffin cups. Sprinkle the tops with turbinado mixture, if using.

Transfer to the oven and bake for 7-8 minutes then immediately turn the oven’s temperature down to 350 degrees F (without opening the door!).

Bake for an additional 10 to 12 minutes, or until the tops are nicely browned and domed and toothpick inserted on top comes out clean.

Let the muffins cool in the pan for 10 minutes then remove and allow to cool on a cooling rack.