This has been discussed at considerable length a number of times here in the past: search through the "Digitrad and Forum Search" on the main Forum page for soul cake, or souling song.  PP&M's rather silly spelling appears to be unique to them, but a soalin, with or without hyphen and/ or apostrophe, will return some hits.  Material in the Forum is now considerably larger than that in the DT, and errors and omissions are often corrected here long before they can be incorporated into the database proper.  Please do try a search before starting a new thread.