Preheat your Belgian waffle maker according to manufacturer instructions. If your iron has temperature settings, set it to medium-high heat.

In a large bowl, whisk together the flour, dark brown sugar, baking powder, baking soda, pumpkin pie spice, and sea salt until thoroughly combined.

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

In a clean glass or metal bowl, beat the egg whites with a handheld mixer on high speed until stiff, glossy peaks form (about 2 to 3 minutes).

Pour the pumpkin wet mixture into the dry flour bowl and stir gently with a spatula just until barely combined (a few lumps are completely normal; do not overmix).

Gently fold the whipped egg whites into the batter in two additions using a wide silicone spatula until no white streaks remain. This step creates the signature light, airy interior.

Lightly brush or spray the waffle iron plates with melted butter or oil. Ladle about 1/2 to 2/3 cup of batter onto the center of the preheated waffle maker, close the lid, and bake for 4 to 5 minutes until deep golden brown, crisp on the edges, and steam stops escaping.

While waffles bake, beat the softened butter, maple syrup, and cinnamon in a small bowl until fluffy and pale.

Transfer baked waffles to a wire rack or directly onto warm plates. Crown immediately with a scoop of whipped cinnamon maple butter, drizzle generously with warm pure maple syrup, and scatter with toasted pecans.