LONDON – A British sandwich chain is becoming popular with U.S. consumers. Pret A Manger reported record sales last week, mostly thanks to its growing American business. During 2015 Pret opened six new locations in the U.S., bringing the total to 65.

The U.K.-based chain says that the United States was its fastest growing market last year, achieving +13.8% like-for-like sales growth, driven by improvements in the quality of ingredients and innovation in salads and breakfast items. Opening larger shops in prime locations has also helped to grow sales, such as a new location at Penn Station in New York City.

Clive Schlee, CEO of Pret A Manger, praised the company’s U.S. operations for a successful 2015. “These results represent another year of record sales for Pret. The highlights were a strong performance in the U.S.—our newly opened Penn Station shop has the highest sales per square foot of any Pret in the world,” he said.

CNNMoney reports that Pret A Manger’s U.S. business has grown into a $200 million operation since the launch of the chain’s first sandwich shop in New York 15 years ago. Schlee wrote in a blog that the company had to adapt to succeed in the U.S. market, such as allowing Americans to customize their hot beverages and salad dressings. "Americans want to choose their own from a large range, whereas Brits are happy to let Pret decide," he said.

Schlee also said Pret offers more choices in the U.S. because "American customers love to mix and match side items, like side soups, protein pots and single sandwiches."