Roast the beetroots in the oven until tender (1-2 hours).
Let the beets cool and then peel off the skin - it should be easy to rub off with your fingers.
In a blender, combine the beets with a little milk and blend until you have a smooth purée.
In a separate bowl whisk together the eggs and sugar and mix in the cream.
Mix in the beetroot purée until smooth.
Add enough milk to fill the can to a few centimeters from the top.