Blake Shelton and Gwen Stefani turned up the flirtation on The Voice during Amy Vasal’s sultry rendition of Drake’s “Hotline Bling,” which reminded them of their own performance on The Tonight Show. Blake couldn’t resist teasing Gwen about their past collaboration, while their playful banter had Adam Levine fanning himself and Pharrell giggling. Let’s watch the video to see how the couple’s chemistry continues to shine on stage…