Bring the milk to a boil with the salt and then bring down to a simmer. Slowly stir in the cream of wheat and let it thicken. Make sure to keep stirring. Meanwhile, whisk together the egg and sugar. Add in a ladle of the cream of wheat mixture to the egg yolk and stir continuously until combined. Add it back into the pot of cream of wheat and stir. Continue to cook until thickened to your liking and stir in the butter. Sprinkle with cinnamon.