For 'a trivial thing' we would say something like peth dibwys. Any of the on-line dictionaries we mention in the pinned discussions will give a couple of options.
It's a traditional British dessert. There are lots of variations but this recipe looks more or less like the one my family uses. http://amandascookin.com/traditional-english-trifle/
A web search will find recipes and pictures for anyone who is unfamilar. Make one and taste it!