Yes totally! Frozen dandelion would just need to be thawed. I like dried dandelion roots for teas and infusions, you could certainly add it to soups and stews. Perhaps you could re-hydrate dried dandelion root by soaking it in a small amount of water and then cooking it in a quiche. I think you could use dried dandelion leaves in this dish as it would re-hydrate some in the baking, but you might also soak them for a short time first. I have dried leaves from other plants that I like to use in soups and stews as well. I'd like to hear your results if you try it!