Using my old pottery mould

Hello Lindsey I have a very old pottery mould with a shell design inside it. I have checked Delia's recipes and am hoping that you might be able to suggest one for me. I think it needs a fish recipe that is more of a jelly/mousse. I have tried a few and they failed to properly fill the mould design so that when it was tipped out of the pot it was rough and had unfilled gaps because the ingredients were not finely processed enough. I wonder if you can suggest one that I might use, be it vegetable or fish, or sweet that I could convert. The mould takes 1 1/4 pints : 25 fluid oz. : 700ml to the rim. I have a photo and could send it to you via the Facebook page. Many thanks in anticipation. Mary