Preheat oven to 200 degrees F and a waffle iron to medium-high heat. Lightly oil the top and bottom of the waffle iron or coat with nonstick spray.
In a large bowl, combine flour, sugar, baking powder, baking soda, pumpkin pie spice and salt.
In a large glass measuring cup or another bowl, whisk together buttermilk, pumpkin puree, eggs and butter. Pour mixture over dry ingredients and stir using a rubber spatula just until moist but slightly lumpy.
Pour a scant 1/2 cup of the pumpkin mixture into the waffle iron, close gently and cook until golden brown and crisp, about 4-5 minutes; keep warm in oven.