Scala, Spark. Fun stuff. I used the resources listed below:
Advanced Analytics with Spark, 2nd Edition - a great cookbook for Spark 2.0+
Functional Programming Principles in Scala - on Coursera with Martin Odersky himself
Twitter's Scala School - a quick and dirty intro to Scala syntax, more suited towards programmers with some Java experience
underscore.io - a collection of free, high quality ebooks