Tortilla de manzana is a traditional apple omelet originating from Asturias. It's made with a combination of eggs, sugar, butter, olive oil, and (ideally) Reinetas apples. If unavailable, these Asturian apples can be replaced with Golden Delicious apples.
The apples are cut into wedges and sautéed for up to 20 minutes until soft and lightly browned on the sides. Once done, they're sprinkled with sugar. The eggs are beaten, then added to the pan with the apples, until the eggs set at the bottom.