It’s important for the butter to freeze as quickly as possible in order to avoid separating. So keep your storage container in the freezer before filling it, and be careful not to heat the coconut oil more than you absolutely have to.
I highly recommend cashew cream; if you use a different kind of non-dairy cream, I can’t guarantee the results: the taste and possibly the texture will be different. And you definitely can’t use milk with this recipe – if you do, you’ll need to add a thickener like xantham gum or lecithin.
You can use a regular blender rather than an immersion blender, but I find it tricky with such a small amount, so you might consider doubling or tripling the recipe, especially since the butter keeps well in the freezer.
Finally, you can use this pretty much like regular butter: for frying onions, for baking, for pie crust, and of course you can leave it out on the counter for half an hour or so to soften, then spread it on warm bread and watch it melt. (Put the softened butter back in the fridge and it will resolidify.)
*Unrefined coconut oil is raw but will impart a slight coconut flavor to your butter. If you’re not worried about it being raw and don’t want a hint of coconut, use refined coconut oil, which is flavorless.
**If your kitchen is hot, your coconut oil will already be liquid, so you can skip this step.