Preheat oven to 450° F and lightly grease a muffin or popover tin.
In a medium bowl, combine eggs, milk, and vanilla extract and whisk until thoroughly combined.
In a small bowl, combine all-purpose flour, sugar, salt, and cinnamon. Whisk to combine. Pour the dry ingredients into the wet mixture and whisk until there are no lumps in the batter. The batter will be fairly thin.
Divide the batter into the prepared muffin or popover tin using a 1/4 cup measuring cup or ice cream scoop.
Bake for 15 minutes, then reduce the temperature to 350° F and cook for an additional 15 minutes, or until puffy and golden brown. DO NOT open the oven to peek while they are baking—the cool air will hit the popovers and cause them to deflate.
While the popovers are baking, melt the butter. In a small bowl, combine the sugar and cinnamon and mix to combine. Set aside.
Remove from the oven and drizzle or brush the tops of the popovers with the melted butter. Then sprinkle the cinnamon sugar mixture over the popovers or dip the tops of the popovers in the cinnamon sugar mixture. Serve immediately.