OAKLAND, Calif. — Would you like that Whopper with or without beef?

This week, Burger King is introducing a version of its iconic Whopper sandwich filled with a vegetarian patty from the start-up Impossible Foods.

The Impossible Whopper, as it will be known, is the biggest validation — and expansion opportunity — for a young industry that is looking to mimic and replace meat with plant-based alternatives.

Impossible Foods and its competitors in Silicon Valley have already had some mainstream success. The vegetarian burger made by Beyond Meat has been available at over a thousand Carl’s Jr. restaurants since January and the company is now moving toward an initial public offering.

White Castle has sold a slider version of the Impossible burger in its 380 or so stores since late last year.