blend normals and roughness material function?

I have been having a go at trying to create sss skin in udk. I noticed in the udk documentation tutorial that i should use this to blend my roughness map and normals map.

However I dont see this in the material editor :S Where do I get it?

https://docs.unrealengine.com/latest/images/Engine/Rendering/Materials/HowTo/Human_Skin/HS_Normal.jpg

The blendnormalsandroughness node is a custom material function.
create a separate function in the content browser by right clicking and going to Materials and Textures> Material Function.

You can copy and paste this function node from the content examples SkinRendering Map skin>materials>SkinMaster