So how to base for Frostgrave? Without really thinking about it, I used a mixture of finely crumbled cork and Vallejo's Sandy Paste: prime gray, wash with Vallejo European Dust, and drybrush white. Very simple and - to my eyes at least - very effective for bases fully covered in snow.
|L: finished; R: primed and washed|
Bits of cork help to vary the texture. I also like to "tease" up the Sandy Paste while it is fresh then tamp it back down after it has been drying for a while. The idea is to create thoroughly frozen, dirty terrain rather than the fluffy stuff you might see freshly fallen in a more temperate climate. Needless to say, grass clumps will not be necessary.