This might be the best programming book I've read to date. I'm probably a tad biased as I love the Elixir language and its ecosystem, but I think the Phoenix framework is simply elegant and powerful. The authors really did a great job at providing just the right amount of context and explanations needed as they take you on a journey to build a modern web-app.
They give you a great overview of how you can get up and running in little time, and how you can extend your application with more modern functionality such as channels and web-sockets, or the lightweight, self-healing GenServer processes. Coming from Ruby, and having a lot of experience with the Rails framework, I'm amazed at how transparent and accessible Phoenix turns out to be.