(NEW YORK) — Burger King is planning to extend testing of its meatless “Impossible” Whopper and will roll out the vegetarian option nationwide by the end of the year.Burger King announced its collaboration with Impossible Foods, manufacturer of the plant-based Impossible Burger, in November.The vegetarian patty is made with mostly soy protein but also contains potato protein, coconut oil, sunflower oil and heme, according to Impossible Foods. The flame-grilled burger will also be topped with tomatoes, lettuce, mayonnaise, ketchup, pickles and white onions.The fast food chain began testing the new menu item at dozens of St. Louis locations earlier this month. The test went “exceedingly well,” and testing will extend into additional markets “in the very near future,” a Burger King spokeswoman told ABC News.Burger King is targeting to make the Impossible Whopper available in its thousands of restaurants in the U.S. by the end of 2019, the spokeswoman said. Copyright © 2019, ABC Radio. All rights reserved.