When I was in France  last month I also made my own paperclay. As it is a bit messy I preferred to make it in France and not in my own tiny atelier. I had some pieces which were not suitable for firing after drying and kept those to make paperclay. Of course you can buy ready made paperclay, but this way you can reuse failed pieces (so long as they have not been fired)  and create something new with them. I do like working with paper clay and paper porcelain as it stronger due to the fibers.

The recipe is easy:
1 empty box for 6 eggs
750 grams of dry clay
0,5 liter of warm to hot water
Tear the box to small pieces and put in a bowl, add the hot water and mix well. 

Grind to dry clay to as fine a powder as possible. 
I just batched it with a rolling pin until it look like this:

Add the powder clay to the paper slush and mix well.
If you want you can add a stain at this point. In this case the clay is antracite clay so not much use to add a colorstain to it, but works well for porcelain and white clays.
Put all unto a slab of plaster (you can make this yourself or buy ready made from some DIY stores), which will suck out the moist. Leave it to dry and turn if need be.
I left mine to dry overnight and there was no need to turn, there will be if you leave it out in the sun.
Once it’s dried to a consistency you are happy to work with kneed it and store it air tight.