Established by 17-year-old Joe Papa in 1912, Papa’s Tomato Pies has been making Trenton-style pizza for three generations. Papa’s grandson Nick Azzaro is now in charge of what he claims to be the oldest continuously-family owned pizza restaurant in the U.S.

The title of America’s first or oldest pizza restaurant does have another claimant. Papa’s founding in 1912 would certainly seem to give it legitimacy, but Lombardi’s opened in 1905 on Spring Street in lower Manhattan, five years before Papa’s. Lombardi’s is credited with creating coal-fired New York-style pizza and lays claim to being “America’s First Pizzeria.” But Lombardi’s closed for a decade in the mid 1980s, re-opening in 1994 at a new location down the block from its original site.

Before this tidbit of history came to light in 2011, the signs at Papa’s used to proclaim it as “the second oldest tomato pie restaurant in the United States.” After a customer told Azarro about the decade that the lights were out at Lombardi’s, he made new signs touting it as the “oldest continuously family-owned” pizza joint.

Papa’s itself has moved locations three times in its history, from its Trenton birthplace on Butler Avenue to Chamber’s Street a few years later, and then finally to its current digs in 2013. Both Lombardi’s and Papa’s seem content with the current truce.

But what about the pizza?

Just as Lombardi’s was an innovator of New York-style pizza, Papa’s was an innovator of Trenton-style pies. A Trenton tomato pie is prepared with the toppings upside down. First, the mozzarella cheese and toppings are placed right on a thin-crust dough. Then the tomato sauce, which is reportedly made from crushed plum tomatoes, is ladled on top. Slide the pie into a well-seasoned oven until the perfect level of char is reached, and then serve to hungry diners.

Because the sauce is on top of the pie, Trenton pies accentuate the taste of the tomatoes. As an added bonus, there are no worries about cheese sliding off the top of a slippery slice.

Papa’s specialty takes the Trenton pizza one step further. Its “mustard pie” is slathered with a layer of spicy brown mustard right on the dough before the cheese, toppings, and tomatoes are added. The resulting pie takes the whole concept of pizza in an entirely unexpected direction. Papa’s menu itself states that some people won’t get it, but regulars know that the right toppings, especially garlic and sausage, really shine with the subtly nose-tingly kick of the mustard.

Papa’s didn’t invent the mustard pie. A German family, the Schuster’s, operated a pizzeria in Trenton until the 1980s, and their specialty mustard pie was a cross-cultural blend of Italian and German flavors. After Schuster’s closure, a customer—or maybe a former Schuster’s employee, the story varies—asked if Papa’s could replicate the mustard pie. Papa’s ran with the idea and made it their own, and now lay claim to be “The Home of the Mustard Pie.”