After looking over numerous sets of instructions that involved long lists of things like "mosaic glass cutters" and "protective masks". My sister and I decided to just wing it.
We went to the local hardware store and purchased a 60lb. bag of concrete for about $6. We struck out at Goodwill looking for china to smash up. The Goodwill by my house is smaller, has a limited selection of "quality" used things (as in, I know someone who found a pair of practically new lululemon yoga pants here!) but this is not the place to get super cheap china that you want to smash.
So, Plan B. We walked down the block to the to the dollar store and picked up 3 bags of decorative glass stones and a three pack of disposable cake tins. One DIY I read suggested using your regular non-stick cake pans and then just cleaning them out and continuing to use them for cake...I'm the type of person who'd be convincing myself that every cake after that tasted like cement, so I chose to get different pans.
Again, foregoing directions, I dumped some of the concrete mix into a bucket only to discover that all those suggestions about wearing a mask would have been a really good idea.
Past the dust flying every fiasco, we got the cement mixed up super fast, my sister greased the pans with crisco to aid in easy removal and the fun making mud pie part commenced.
PS. If you're feeling to lazy to figure it all out yourself, you could just buy a kit. I used these a few times with kids I took care of in college. Super easy and really fun, just watch out if you happen to be with a small person who thinks putting your keys in as decoration would be hilariously funny. Trust me, it is not.