In a medium pot, combine the whole milk, lemon peel, orange peel, and cinnamon stick. Bring to a gentle boil, then remove from heat and let steep for 15 minutes. Strain and reserve the infused milk.

In a separate bowl, whisk together ½ cup of reserved milk, cornstarch, and all-purpose flour until smooth.

Pour the infused milk back into the pot, add the cornstarch mixture, and cook over medium-high heat while stirring until thickened, about 6-7 minutes.

Pour the thickened mixture into a parchment-lined baking dish, smooth the top, cover with plastic wrap, and refrigerate until set, at least 3 hours.

Cut the chilled mixture into squares. Prepare bowls with beaten eggs, flour, and a mixture of sugar and ground cinnamon for coating.

Heat sunflower oil in a skillet over medium heat. Dip each piece in flour, then eggs, and fry until golden brown, about 2-3 minutes per side.

Remove the fried leche frita, drain on paper towels, and toss in the sugar-cinnamon mixture. Serve warm.