Preheat oven to 450º.
Grease pan with butter and heat pan in oven while prepping batter.
In a mixing bowl, gently beat eggs with a whisk attachment.
Whisk in flour, milk, teaspoon of cinnamon, and teaspoon of sugar just until a smooth batter forms. Do not over-whisk.
Carefully pour batter into the heated popover pan, filling halfway.
Bake for 20 minutes. Then, reduce heat to 350º and bake for another 20 minutes. Do not open oven until baking is through!
Remove popovers from pan. Allow to cool for a few minutes. Then, while warm, roll in cinnamon and sugar mixture.
Serve warm with butter or dulce de leche.