Burger King, known for meaty excess like its Bacon King sandwich, is now selling a plant based burger. Burger King announced a test run for the burger in 59 restaurants in the St. Louis area. Burger King says the sandwich will use patties from Impossible Foods. Burger King is taking its signature sandwich, the Whopper, and creating a vegan version.

The Impossible Whopper is flame grilled like the regular Whopper, and comes with the standard tomatoes, lettuce, mayonnaise (vegans hold the mayo), ketchup, pickles and onion.

The move underscores how chains are looking for new ways to gain an edge over rivals as competition heats up — and the rapid growth in demand for meat alternatives.

Impossible Burgers are designed to mimic meat using the company’s novel “magic” ingredient, heme, produced with a special kind of yeast. Impossible Foods, part of a growing crop of meat substitute producers, has sold its burgers at restaurants since 2016, starting with trendy eateries like David Chang’s Momofuku Nishi in New York and Jardiniere in San Francisco, and now served at over 5000 restaurants across the US.