Mix equal part sand and plaster of Paris in a gallon Ziplock bag, with enough water to make a moist clay consistency. It's a little too crumbly in this photo, and not quite enough. This was actually the hardest part for us.

We used a 12 oz plastic cup for measuring and based on that would recommend 3 cups each of sand and plaster, and about 1- 1.5 cups of water.

You have to work pretty quickly because the stuff starts to set up fairly fast, and starts getting crumbly.

Pack the mixture in firmly, until the can is about 3/4 full, then dig out a 1.5 inch diameter cavity (we used a plastic spoon), leaving about 3/4" plaster/sand lining the can.* Carve a wider hollow towards the back (bottom) of the can, to create a better heat retention area.

Run a tool, or the back of your plastic spoon through the iron pipe nipple to clear out the plaster there. Wipe the outside of the whole thing clean with a wet paper towel, and then let it sit for a half hour.

*Alternatively (it occurred to us later), you can probably stuff the nipple with paper, and insert a toilet paper tube into the center of the can, or something similar, and pack the plaster in around that, then either remove it or let it burn when you turn on the torch.