I've never seen anything with both yeast and baking powder. What's the reason for that? Shouldn't e.g. muffins get even more fluffy by adding some yeast? Or bread by adding baking powder? I know there ...
Both yeast and baking powder are used to gas-fill the pastry, make it expand and thus make it soft and fluffy. Using yeast is rather inconvenient - it can be dead already or if the yeast is submerged ...