M&S Ultimate Brioche Burger Buns Delicious and light, these buttery brioche buns are the perfect choice for gourmet burgers. Richly flavoured and glazed with egg yolk for the perfect finish. Contains a natural source of Vitamin D and fibre. Four 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.