what do I do for dry milk that is hard

We have some large bags of powdered milk that are still good except that they have gotten hard like a brick. Does anyone know a way to get it softened up and more powdery? I have tried putting it in a bag and pounding it with a hammer, and I was even wondering about running it through the meat grinder or the grain mill. But I wondered if there was a non-mechanical way. I know when brown sugar is hard you can put a piece of bread in it, and as the bread dries the sugar softens. I guess I'm wondering if there's any reason not to do that with milk.

I would think that desiccate might help, or sticking it in the oven to further dry it.

I used to break it into chunks with an ice pick and then put it in the food processor. It worked pretty good.