Frost Core

The drop itself is not in question. Every Ice Golem hands one over, so luck plays no part. The bottleneck is getting them to appear at all, and that is weather. They only walk out while a Blizzard is running, and only on the surface of a snow biome, so you are waiting on the sky rather than grinding a spawn rate.

That makes the setup simple. Flatten a long stretch of snow surface, put a bed and a couple of campfires at one end, and go do something else until the storm rolls in. When it does, stay above ground and keep walking the flat. Golems are slow and easy to read, and they keep arriving for as long as the weather holds.

If you want everything the cores build, plan on more than one storm. A single blizzard rarely lasts long enough to cover it.