In the case of what versus which, though, it comes down to a matter of specificity.
The word what is used with more general ideas:
What should I make for dinner with this arugula, sea bass, marshmallow whip, gnocchi, and macadamia nuts?
It’s a general musing about the vast culinary potential for those ingredients. Contrast that with the following:
Which of my half-dozen recipes featuring arugula, sea bass, marshmallow whip, gnocchi, and macadamia nuts should I use for my dinner with Andre?
In this case, there is a finite number of possibilities, so which would be used.