For the past week or so we have had some real winter here in Southern Finland. Temperatures between -5 and -10 celsius. When I was a kid we use to make these every winter (my parent still do from time to time) but for some reason I have never really done one all by myself. So it was about time to try, and they turned out perfect, if i may say so myself.
They are really easy to make. Just take a normal plastic bucket full of water and leave it outside. It was -7c and this was outside around 20 hours. Hole idea is that water is frozen on the sides but not inside.
Trying to get that water out is the only "tricky" part. You might need to make a small hole on the roof to get the water out and the candle in.
Take care