Prepare a large boiler or saucepan by filling 2/3 - 3/4 with water. You want enough room for the pudding to be able to move around in the water as it's cooking. Put on the stove and bring water to boil.
Soak a clean calico pudding cloth in another bowl of boiling water from the kettle for 5 minutes.
Wring out excess water (you may need gloves or use a clean tea towel wrapped around the pudding cloth) and spread out pudding cloth on kitchen bench.
Use about 1/3 cup plain flour and sprinkle in a 30-40cm diameter circle. Make sure flour is most concentrated towards centre and lighter towards the outside of the circle. Rub flour into the cloth.
Pour pudding mixture onto centre of cloth. Pull the edges up and work into a nice round shape. Make sure there is no gap at the top where you've gathered the edges together.
Secure the gathered edges as close to the pudding as possible with kitchen string. Secure well and make sure there's a loop so you can hand the pudding to dry out once it's cooked.
Place pudding in boiling water and boil for 3 1/2 hours. Make sure the water continues to boil and you keep it topped up with additional water if necessary. (Boil a kettle and add boiling water rather than cold water from the tap to ensure a continuous boil.)
Once cooked, hook string from where you've secured the pudding cloth into a wooden spoon and gently lift from the boiling water.
Hold over the sink or somewhere that the pudding can drip a little. Within a minute or so you should see the pudding cloth drying in spots.
Hang the pudding somewhere safe and dry for one day to cool and dry out.
After a day of drying out, take the pudding down. Cut open the ties and take a look at the top of the pudding. You should see a skin has formed around the pudding. Scrape away any excess flour from the top of calico pudding cloth and tie to secure again.
Leave the pudding out (no need to hang again) in a dry place for a couple of days to dry out completely.
Store pudding in fridge (still in cloth) until ready to be re-heated.
To re-heat, take out of fridge and leave to stand for 6-12 hours. Immerse in a pot of boiling water for 1 hour and then hang for half an hour before cutting away ties and gently unwrapping the pudding. Invert onto a serving plate and enjoy with custard.