Preheat your Belgian waffle maker to medium-high heat. In a large bowl, whisk together the flour, brown sugar, baking powder, baking soda, pumpkin pie spice, and fine sea salt until evenly blended.

In a medium bowl, whisk the pumpkin puree, buttermilk, melted butter, egg yolks, and vanilla extract until completely smooth.

CHEF SECRET STEP: In a clean glass bowl, whip the 2 egg whites with a handheld whisk or mixer for 2 minutes until soft peaks form. Whipping egg whites separately is the secret to an ultra-crisp exterior and cloud-like fluffy waffle interior!

Pour the pumpkin-buttermilk mixture into the dry flour bowl and stir with a rubber spatula just until combined (small lumps are totally fine; do not overmix!).

Gently fold the whipped egg whites into the batter in two batches using gentle sweeping motions until no white streaks remain.

Lightly brush or spray the hot waffle iron with oil. Pour about 1/2 to 2/3 cup of batter (depending on your iron size) into the center and close the lid.

Bake for 4 to 6 minutes, or until steam stops vigorously escaping from the sides and the waffles are deep golden brown and audibly crisp. Transfer to a 200°F (95°C) warm oven rack while cooking the rest.

Whip the softened butter, maple syrup, and cinnamon together in a small bowl until fluffy. Serve hot waffles topped with a generous dollop of spiced maple butter and warm maple syrup!