Can someone identify this herb?
I don't think it's shiso, as that tends to have a more jagged edge.  I suspect it's the botanically related Korean kkaennip (aka 'sesame leaf', which is also of the family Perilla):


http://www.seriouseats.com/2011/07/seriously-asian-perilla-leaves.html
http://www.maangchi.com/ingredient/perilla-leaves


(but I can't discount bitter leaf, as that's not something I'm familiar with)