Position a rack on the lowest rung of the oven and preheat the oven to 425ºF.

Butter or spray nine ¾ cup glass custard cups or ten ½ cup muffin cups. For the custard cups, place them on a half-sheet pan. For the muffin pans, use two to give the popovers room in between for air circulation.

Pour al the ingredients into the container of a blender, food processor, or with a hand mixer and mix until smooth. Strain if lumpy.

For the custard cups, pour 1/3 of batter into each cup, dividing any extra batter among the cups. For the muffin cups, use ¼ cup of batter for each cup, filling alternate cups in each tin.

Bake, without opening door, for 25 minutes, until the popovers are puffed, browned, and crisp on the outside. Turn the oven down to 350ºF and bake for another 15 to 20 minutes, to help dry out the interior, which will still be a little custardy.

Mix the sugar and cinnamon in a medium bowl. Thoroughly brush each puff all over with melted butter, then dredge in sugar and cinnamon mixture to coat completely. Let cool on a baking rack.

Serve immediately.