Serendipity in NYC

Hey girls....so I'm taking my 13 yr old niece for a girls day at Serendipity in NYC this Saturday. I think we'll probably just do desserts because I know that's what they're famous for. I had my heart set on a frozen hot chocolate because I've always heard about them but I just read that they aren't much to write home about. Has anyone ever been there and could reccomend what we should get? If I'm not paying for actual food, I dont mind spending a little more and ordering more than one dessert.

We are true New Yorkers and because of that we've never been there. Haha I know it's very touristy but i was looking for something different for us to do. Any recommendations on what to order?

Thanks in advance!