On one thing, perhaps, we can agree: anyone grabbing a bottle of yellow mustard from the fridge and squirting it all over a plain ol' pizza is just a troublemaker. We'd say the same if the deed were done with ketchup, even though it's way closer to most pizza sauce on the condiment family tree. But what about mustard as a deliberate pizza topping?
A debate to supplant the ongoing pineapple wars has been raging ever since the world outside of New York City learned about a place called Lions & Tigers & Squares...
...sorry, that was obligatory. Anyway, they have a Reuben sandwich inspired pizza with corned beef, sauerkraut, and yes, mustard. Co-founders Sal and Francis say they were inspired by a place in Trenton, NJ called Papa's Tomato Pies, where a drunk customer slurred his words in asking for a mushroom pizza, and was given one with mustard instead.
It's not a totally unprecedented combination: Pizza Hut went through a phase of putting hot dog bites in the stuffed crust pizza, and provided some of the yellow stuff for dipping. And you can't really say that any dough self-described as "pretzel crust" doesn't call for mustard as well. It's the "crime" of replacing red sauce that really seems to be the point of contention here. And the genius of making a Reuben sandwich into a pizza outweighs any consternation -- though some brave soul really needs to add a layer of Swiss cheese and Russian dressing on top.
It's like pineapple, which only works if you pair it with hot peppers for the sweet/spicy mix. Mustard is contingent upon the appropriate supporting ingredients. Am I wrong? Tell me why in comments below.