When I was younger Harriet the Spy was one of my favorite books. I would read it over and over and over again. One detail I had completely forgotten about was one of her favorite treats, egg creams. I had no idea what they were. I hated eggs (still do) and this sounded like something egg-y so I'm pretty sure I was a little horrified at the thought.
Turns out it's a real thing. An egg cream. And it sounds delightful.