Put all the ingredients, together into a bowl and beat to a smooth batter.
Sprinkle the cinnamon over the top.
Bake for 45 minutes at 175°C.
It sinks and becomes denser as it cools. If you eat it hot, you'll need a spoon to scoop up the soft custardy tart, but cold you can pick up the slices in your hand, if it hasn't vanished long before then.