Using a wire whisk, combine the milk, cornstarch, sugar, lemon peel and cinnamon stick in a 1 1/2 quart saucepan. Bring the mixture to a boil while whisking, then lower the heat and continue to whisk for 10 minutes. Whisk constantly so the mixture does not scorch.
After the 10 minutes of whisking, the pudding mixture should be very thick. Remove and discard the lemon peel and cinnamon stick. Pour the mixture into a 9-inch-by-4-inch ceramic or glass loaf pan, and allow to cool for at least 24 hours uncovered on your kitchen countertop.
When your pudding mixture has cooled and dried completely, cut into 12 equal sized squares.
Prepare three shallow dishes to use when dredging your leche frita. Fill the first dish with the flour, scramble the eggs well in the second dish, and fill the third dish with the panko.
Heat the vegetable oil in an 8-inch skillet over medium heat. Pass a square of the leche frita though the flour, then coat with the egg, and then pass through the dish of panko breadcrumbs.
Using a slotted spatula, carefully place the uncooked square of leche frita in the hot vegetable oil, and fry until golden on one side, about 1 minute. Carefully turn to the other side, and fry for another minute. Remove the leche frita to a pan lined with paper towels to cool. Fry all of the squares in the same fashion. Serve warm.