I have found a few references to Jelly Trowels, but they are few and far between. I have been unsuccessful in finding a reliable source that would explain its use. However, an elderly lady told me that it was used to serve a dessert made of whipped jelly made in copper molds and served chilled. Having no other story to go on, I'll add that two cents worth. They are interesting pieces.
(Jelly Trowel shown in unknown pattern by Dominick and Half)