I got this recipe from someone who works at the National Library of Wales in the book binding department. I was told it is traditionally used to stick the leather to the hard cover of the book (usually called the case). It also is a great substitute for PVA when sticking paper together, or making paper-mache.
Add 60g of flour (not self-raising) to 500ml of water in a saucepan. Pour it in slowly while stirring to avoid lumps. Bring the mixture to the boil then turn the heat down to let it simmer for 5 minutes.
Afterwards let your new glue sit until cold. It will only keep for a few days so use it quickly. To stop it drying out put the glue in a container add a little water, it should just sit on the top, don’t mix it in. Seal the top and leave it.
For alternative methods and helpful tips visit this page. Rhonda’s website is a great resource for anyone interested in bookbinding.