Preheat the oven to 180 ºC (350 ºF).
Using your hands, mix the orange zest with the sugar, rubbing it until the sugar takes on an orange hue and a strong orange aroma.
Add the flour and baking powder to the flavored sugar and mix well.
In a separate bowl, beat the eggs with the orange juice and melted butter until you get a smooth mixture.
Combine the flour and sugar mixture with the wet ingredients and mix until you get a consistent, smooth batter.
Grease a baking pan well with butter or oil, line it with parchment paper, and grease the paper as well.
Pour the batter into the pan and lightly tap the pan on the countertop to remove air bubbles.
Bake for about 20 minutes, or until the roll cake is fully cooked. To check if it’s done, insert a toothpick into the center — if it comes out clean, it’s ready; if not, bake for a few more minutes.
Lay a clean kitchen towel on the countertop and sprinkle it with sugar.
Once the roll cake is baked, flip it onto the towel and carefully remove the parchment paper.
Sprinkle a little more sugar on the surface of the cake.
With the help of the towel, carefully roll the cake, pressing gently to form a tight cylinder.
Store in the fridge for a few hours, wrapped in the towel, to set.
When ready to serve, carefully remove the towel and place the roll cake on a serving plate.
Decorate with orange slices, mint leaves, and/or powdered sugar.