On a server I was on, people were able to use brews to make other brews.
How do I do this?

I tried assigning a brew to a custom item (i.e. having the material = potion and the name = ), but that doesn't seem to work. Neither does just putting the brew name into the ingredients list.

Does anyone know what I can do?

@Sn0wStorm

Config.yml contains an example of using a brew in another recipe, see screenshot. You can even specify the amount.