When it comes to sausage rolls, I am a disciple of the Holy Trinity (mustard, onion, ünd sauerkraut). I will admit, however, that I’m known to add a few lashings of mayo to the freshly toasted inside of the roll.
Not sure if that’s orthodox by any culinary tradition and I don’t really care. At least I’m not a devil worshipper (i.e. person who puts ketchup on their sausage).
Or any cured or smoked meats. I like ketchup on roast beef, but pastrami & sausages gets mustard, preferably horseradish mustard. I watched in horror as we took a relative to the venerable house of meat worship on Houston Street called Katz’s Deli and she ordered a reuben with mayo. Now, I’ll have a salami & cheese sandwich myself, but out of respect for that unworldly meat and my ancestors, Katz’s pastrami should not be served with cheese or mayo.