Preheat the oven to 180 º C.
Bring the milk to a boil with the lemon peel and the cinnamon stick. Set aside.
Separate the whites from the egg yolks. Beat yolks with sugar for a few minutes until it is a paler color.
Add the flour and fold it into the mix.
Slowly pour the milk on the yolk mixture, stirring occasionally with a spatula, until it thickens.
Transfer this cream to a bowl and let it cool down.
In the meantime, beat the egg whites to stiff peaks in the mixer.
Carefully fold the egg whites into the yolk cream, leaving you with a smooth mixture.
Distribute spoonfuls of this mixture in a deep clay dish traditionally used for sericaia. Dust the top generously with cinnamon powder.
Bake for about 50 to 60 minutes - test it with a skewer. It should come out clean in the edges, but still slightly moist in the center.
Let it cool down and serve with the plum jam.