Add sugar and cinnamon in a plastic bag and shake until thoroughly combined; set aside.

Pour oil into a deep pot over medium-high heat. When the oil temperature reaches 350 degrees F, add 10 spiral Duros de harina in the hot oil in a single layer and cook until they swell.

When duros de harina is ready, remove from the oil using a slotted spoon and place it on the wire rack.

Sprinkle with the sugar-cinnamon mixture generously and serve immediately.