From the blog:
All you need is a bunch of wine corks and superglue. If you don't have 60 wine corks lying around the house, you can ask your local wine shop, restaurants, bars, etc. I got mine from my local wine shop — they gave me 100 corks. Start by gluing 3 corks together. You have to use superglue and not a hot glue gun. Continue to glue corks to each other until you have a circular shape. It needs to be big enough to rest a pot on top. Once it's, dry, it's ready to use.
Find the full instructions at Sweet Paul.
(Image: Alexandra Grablewski)