First of all, I have to admit that I just stumbled my way through the settings until I achieved the look I was after, so this tutorial is just a retrace of the steps, without the stumbling of course. Where I can, I'll try to give an explanation as to why the settings work.
First we'll need a model. I used a landscape object with these settings. You can use different settings if you like, but keep in mind that the flatter the model, the more areas will be covered with snow. The taller the model the less areas will be covered, so it all depends on the look you're trying to achieve.
Next, in the Material Manager, create a new bhodiNUT NUKEI material and assign it to your object with Spherical mapping. We'll use Surface 1 for the rock and Surface 2 for the snow and blend them with the Fusing channel. Starting with Surface 1, we'll set the colors of the Diffuse and Speculars 1, 2 and 3 to different shades of grey. The "Attributes" sections I left at their default values. See the examples below.
Now disable the Reflection and enable the Roughness. Here's where I just played around with the values until the preview looked like it does in the image below. For a noise Function, I chose Stupl but there are a couple of others that allow you to set the Octaves value and they work just as well. I discovered that the more Octaves you have the more detail showed and the higher the Scale the wider the gullies were. The Amplitude looked better with a negative value and the gullies became deeper the larger that value was. Also, it just didn't look right without Hard Bump and Absolute enabled. At this point you can experiment on your own and see what you can come up with. Below you'll find the settings that I used.
We need to now set up the fusing so we can see the results of Surface 2 as we work on it. For a FUSER Texture, use the bhodiNUT Falloff shader. On the Texture page, create a three color grayscale gradient and move the handles close together like in the image below. Keep the black handle position at around 81. Here again, if you move the handles more to the left, you get more snow areas. Move them to the right, you get less.
The Attributes page. Now here's where I just stumbled around a lot and finally came up with these settings. The idea here was to give the snow a look of thickness where the snow and rock textures meet. Maybe you'll want to come back here and experiment with these values to see what you can come up with.
OK, on to Surface 2. For the snow we'll only use the Diffuse, Specular 1 and Roughness channels. On the Diffuse color, just take a little bit of red out of a white to give the snow a colder look. On the Specular you'll need to set the Attributes to the values below so that the snow has a specular highlight brighter than the default values.
And finally.... the Surface 2 Roughness settings. I chose Wavy Turbulence simply because it sounded like it goes with snow. Here I set the Scale and Amplitude to a value lower than what I used for the rock surface so the snow looks smoother than the rock.
That's it. All that's left to do is set up the lighting, add a sky background and start rendering.