Combine the flour, cornstarch, sugar, baking soda, and pumpkin spice in a medium bowl and stir using a balloon whisk to combine.
Add the wet ingredients: pumpkin puree, buttermilk, and butter; mix until smooth. Careful not to overmix.
Let mixture rest for 10 minutes while the waffle iron is heating up.
Spray a waffle iron with cooking spray and heat until the waffle iron is hot. Cook the waffles in batches until golden brown.
Serve hot with salted caramel or any other topping of your preference.
Make the caramel: In a medium heavy-duty saucepan, combine the sugar, butter, salt, and water. Cook over medium-high heat, stirring until the sugar dissolves and butter melts. Reduce heat to low, stirring occasionally, until the mixture turns golden brown. Remove from heat and very carefully add the cream. Mix well until the mixture looks homogeneous and smooth. Return to heat, stirring constantly, and cook for 1 more minute. Set aside and let it cool until warm.