Show only the latest post in a specific category

This is probably a really dumb question with an obvious answer, but I can’t find it in the codex.

I want to show asides in a sidebar on my homepage. I’ve got that working. The problem is, I only want to show the most recent aside. Short of deleting all older asides or re-categorizing them (fine for little maintenance blurbs, not so fine for actual posts), how do I do this?