Should I use "is" or "are" in the following case?
What I'll never forget, though, is/areis the first days I started noticing her.
What I'll never forget, though, are the first days I started noticing her.
Here, the main topic is those "first days," so I figured I should use "are." However, here I'm also talking about "What" so someone said I should use "is."
What's the correct option?