Since about 10 years, "brunch" is very popular in Paris. Many restaurants and brasseries offer this kind of "half breakfast, half lunch" option. The list below presents the best places with a all-you-can-eat buffet in Paris, with high quality food, from the fanciest place to more budget-friendly options (according to Parisian standards). You would have to book ahead, I recommend at least a week before. Unless otherwise stated, they offer a brunch option only on Sundays. They are all vegeterian friendly, but for vegans, you will miss an important part of the food offered there so I would say it's not worth it for the prices.