The Impossible Whopper is expected to roll out quickly if a test in St. Louis goes well.

Vegetarians may get a taste of Burger King’s Whopper

Burger King is testing a vegetarian Whopper made with the Impossible Burger.

This week, 59 Burger King restaurants near St. Louis started testing the Impossible Whopper. The plant-based patty is flame grilled and topped with tomatoes, lettuce, mayonnaise, ketchup, pickles and white onions on a sesame seed bun, according to a statement.

Impossible Foods is a California-based startup that makes meat and dairy products from plants. The company also provides meatless patties for many other restaurants including Red Robin and White Castle.

If everything goes as planned, the soy-based burger will expand availability of the Impossible Burger quickly to every branch in the country, according to the New York Times. The fast food chain has 7,200 locations.