Preheat the oven to 200 degrees Fahrenheit, with two racks inside the oven and a baking sheet on each rack.
Combine the flour, cornstarch, baking powder, salt, and cinnamon in a large bowl. Set aside.
Whisk together the milk, butter, egg yolks, sugar, vanilla extract, and vanilla bean paste until combined. Pour into a blender and add the chopped plums. Blend at high speed until smooth.
Pour the milk mixture into the flour mixture and stir until combined. Set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites at high speed until soft peaks form. Fold the whites into the batter.
Heat the waffle iron according to the manufacturer's directions. Ladle some of the batter onto the hot iron, (mine takes about 2/3 cup batter to fill the iron perfectly when pressed).
Don't lift it to peek for at least a two minutes after closing it. Cook until the waffle is golden, then immediately transfer the waffle to the baking sheet in the oven. Continue cooking them and placing them on the baking sheet in the oven as they're done, making sure to keep them in one layer and not letting them touch each other to ensure optimum crispness.
Once all the waffles are made, serve them alongside the maple and mascarpone.