I'm looking for a story (almost certainly a modern author working in a fairy-tale motif, rather than an actual folk tale) in which a prince is given a sequence of "impossible" tasks by a princess he is courting, e.g., "bring me a dress made of sunshine" (not sure if this is an exact quote). After completing a series of such tasks, he decides not to marry the princess, but instead marries the witch or sorceress who helped him with the tasks.
The story was in a collection of other stories (not sure if single or multiple authors for the collection), and in a public library in the US by the early 1990s.