M&S 2 Katsu Burger Buns Two glazed white burger buns flavoured with a katsu curry paste and topped with maize. Two per pack. All of our breads are a natural source of Vitamin D and Fibre, two nutrients that are naturally low in our diets. We use a natural source of Vitamin D that is produced by yeast, which is why you will find ‘yeast’ on our list of ingredients, not because we use it as part of the dough making process.