A recent question suggested the tag 'alone-cooking', which I've personally never seen used for the concept.
I have quite a few cookbooks on that general subject, and the terms I generally see are 'solo cooking' or 'cooking for one', but I don't know that either one's obvious enough that people are going to find it right off without a few synonyms. In the case of baking or preserving, I've seen the term 'small batch' used, but I don't know that it necessarily fits for all types of cooking.
(and before we trigger a discussion on how appropriate it is to tag by quantity, I'll point out that cooking for one or two has considerations because of the lack of economy of scale; on the opposite side of the scale, we do have a bulk-cooking tag.)