Schaslich

I realize that this is off-topic but since there is such a huge foreign component to this great website, I feel that I may get a great answer.  The best Schaslich mit Brötchen I have ever eaten came from a small stall in the Offenbach am Main Marktplatz located nearest to the men's toilet.  I only mention this as there are many other stalls in the Marktplatz.  Schaslich is made from kidney meat of either pork or beef.  I don't know which meat this stall uses.  Secondly, the sauce is probably what makes this treat so outstanding.  My wife is from Offenbach and I have continually asked the stall to give me the recipe but they have always refused.  It's a recipe to die for.