The award-winning, plant-based burger from Impossible Foods is now available at all White Castle restaurants nationwide for $1.99. Hailed as “one of the country’s best fast-food burgers, period,” the Impossible Slider debuted in April at 140 White Castle locations in New York, New Jersey, and Chicago.

Based on the overwhelming success of the pilot program, White Castle is expanding availability of the Impossible Slider starting Wednesday to all 377 of its restaurants in 13 states—from New York to St. Louis.

“Our Cravers definitely developed a hunger for the Impossible Slider,” says CEO Lisa Ingram, whose family has led White Castle for four generations. “Sales easily exceeded our expectations. The Impossible Slider is a hit with both loyal ‘Cravers’ and customers brand new to White Castle who are seeking out this buzz-worthy slider.”

For the past six months, Impossible Foods’ scientists have been working with White Castle to ensure that the Impossible Slider works great with the kitchen system of White Castle locations. The Impossible Slider was an instant hit when it debuted in April and remains a social media phenomenon.

More than 60,000 fans have signed an online petition for other fast-food chains to follow suit. Sales have remained above expectations for the past six months.

“White Castle is teaching us how to popularize plant-based meat and become a mainstream, mass market menu item and cultural icon,” says Impossible Foods’ Founder and CEO Dr. Patrick O. Brown. “This partnership is a big win for consumers, with the partnership of White Castle and Impossible Foods.”

The Impossible Slider is topped with smoked cheddar cheese, pickles, and onions and is served on a signature bun available individually for $1.99.