if you go to the unreal marketplace there is a free project called “Automotive Materials.” In that project there is some car paint that sparkles. The sparkles are a lot finer though.
What I’d recommend trying is to use a small-scale noise map and use it as the roughness of the material surface. You might want to remap the values to give you control over how intense the effect is. You then need a very rough normal map which tiles over the snow’s surface. This simulates the fact that snow is millions of tiny facets reflecting light in many directions. Tiling a rough normal map over the surface simulates those many directions.
If you adjust the scale and intensity of the roughness map and the scale of the normal map you should be able to achieve something you like. It might require some adjusting of the Post Processing bloom settings to make the sparkles really stand out.
Finally make sure your base snow color isn’t too bright, otherwise it will be harder for the sparkles to stand out. In your example image you can see the snow itself is mid-tone blue to dark-tone blue in color which lets the sparkles contrast against it nicely.