Place the milk, sugar and thickener in a saucepan over very low heat. Whisk them all together until the sugar and starch have dissolved into the milk, then add the cinnamon and zest.

Continue stirring the mixture over low heat for a few minutes to give the flavorings some time to infuse. Raise the heat a bit and slowly bring the mixture just to the simmer. When it gets hot enough, the mixture will thicken. This tends to happen rather suddenly, so make sure you're at the stove mixing to avoid the mixture forming lumps. (If not, a vigorous whisking should make things right.)

When the mixture is thick and smooth. Remove it from the heat and let it cool for just a minute or two, then pour it into serving bowls or, if you want to get fancy, into decorative molds.

Let everything cool for a good ten minutes or more, then place in the fridge to chill until your biancomangiare is quite thick and perfectly cold. (It can be made ahead up to this point.)

To serve your biancomangiare: unmold onto plates (if using a mold), and top with one or more of the toppings suggested above. Serve while still chilled.