Put the long grain rice in 2 cups of water and let it bubble.
Add the milk and mix well, stirring continuously. When the rice begins to soften, add the sugar and the potato flour dissolved in water. Mix the yolks with the pulp of the vanilla pod and add to the long-grain rice form. When the rice becomes creamy, mix well and remove from the stove immediately (it should still be rather thin, as it will solidify when it cools down). Pour into a suitable bowl and set aside to cool.
Sprinkle with cinnamon before serving.