Bringing your own condiments?
This is a restaurant etiquette question. There's a kosher dairy restaurant in Brooklyn that makes fabulous pancakes (Cafe K), but all they offer as toppings are "syrup" and chocolate sauce. I like orange marmalade on pancakes & waffles. I checked various brands, and I see that Hero preserves from Switzerland have the OU. Would it be appropriate for me to bring an unopened jar and explain my preference, or would that be considered a major faux pas?
Not a faux pas if you speak to someone who is in charge of the Kashrut (verifies the kosherness of the restaurant.) If you frequent the restaurant a lot they may even keep the jar there for you and bring it out when you are there or order jars for the restaurant. I am sure they have other things on the menu that go with the marmalade.
the policy for kosher restaurants is not to allow any outside food in. They cannot make exceptions. Talk to them about their carrying it. Or they may allow you to bring an unopened jar and they will open it at the table for you. But you need to check first with the managment, Rabbi etc