Question on Shaders in Material Functions

So, I have been following a tutorial on how to build a snow material for the landscape actor. The tutorial directs you to select subsurface for the material shader. However, I’m hoping to use the material as a material function, which is what I have been building it as. I plan on using it as part of a material blend in my master landscape material.

I don’t see the option to select a material shader for a material function. Is there a way for me to work around this so I can use it in a material blend?