In a large saucepan, combine whole milk with granulated sugar, cinnamon stick, lemon peel, and orange peel. Heat over medium heat, stirring gently until the mixture comes to a gentle boil, then remove it from the heat. Let it cool for about 15 minutes.

In another bowl, whisk together cornstarch and all-purpose flour with the remaining whole milk until smooth. After 15 minutes, strain the infused milk to remove the peels and cinnamon stick, then gradually mix in the thickening mixture.

Return the combined mixture to the saucepan and cook over medium-high heat, stirring constantly for 6-7 minutes until it thickens to a custard-like consistency.

Cover the dish with plastic wrap and refrigerate for at least 3 hours, or overnight if possible.

Once chilled, remove the set leche frita from the refrigerator, and cut it into squares or rectangles.

Set up an assembly line for frying with all-purpose flour, beaten eggs, and a mixture of sugar and ground cinnamon.

Heat enough sunflower oil in a skillet over medium-high heat. Dip each piece of leche frita first in flour, then in the beaten eggs, and fry until golden brown and crispy, about 2-3 minutes per side.

Remove each piece from the oil and let them drain on paper towels. While warm, sprinkle the cinnamon-sugar mixture generously on top.