Melt the butter in a saucepan and stir in the flour. Gradually add the milk, stirring constantly. Then stir in the sugar. Bring to the boil again briefly and then remove the saucepan from the stove - stir for a few more minutes. Pour the pudding mass into a baking dish or on a baking sheet and allow to cool. Put the cooled mass in the refrigerator. Dust with cinnamon before serving.
Tip: The pudding tastes best if it was made the day before serving.