This type of container is to me the quickest way to make high quality containers there is. It has the limitation that it is to a great deal only usable in spring and summer. After the bark has been folded you have a ready made container. To make it more durable and useful however, it is an advantage to dry it before you do the final steps. Otherwise you will experience curling and shrinking of the bark, making the construction loose and without a great fit.
First choose a section of Aspen (or specie with bark of similar structure) which is fairly straight and knot free. Score around the tree in the top of the piece you want, and do the same in the bottom. Then score diagonal line connecting the other two. Make sure you score all the way into the wood. You will kill the tree anyway, so there is no reason to be careful.
I use my flat moose antler wedge to pry loose the bark.
Determine the middle of the sheet by using a folded line. I have no picture of the process, only the curled sheet.
Score a shape across the sheet, resembeling the cross-section of a convex lense. I did this on free hand this time, but to get a more regular and beautiful shape you could make a simple birch bark pattern.
Fold it over and pull it over a log stump, bind around and leave it to dry. This is to prevent it from curling inwards. Not very easily achieved primitively, so I am currently testing another method, which I have never seen demonstrated anywhere. If it works out well, it will be presented in a book.