I've been wondering about this! In all the years I've had links with Italy and Italian people, and in all the years I've lived here, neither I nor my friends, nor the people on the Italian cookery newsgroup I follow have ever heard of this. As a linguist, I quite understand that it may well be a word invented by Italian emigrants to other countries such as Britain, the USA and Australia. But the members of my Italian newsgroup have never heard of it. Inventing words that have some of one language and some of another is quite common in immgrant communities. To identify exactly what Sompanelli really are it would help if one knew the recipe. So far we only have 'batter', and there are several versions of that in Italy, so in order for me to research a bit better so that I can send some cogent information to you, those details would help greatly. You've got me fascinated!
Enough is never as good as a feast Oscar Wilde