This photograph was taken in my garden in the UK so all the Italians who don't believe that porcini grow anywhere other than the hallowed ground of Italy, look with envy at the evidence.
As you can see the porcini grow to be quite large here as they are left in the ground to do so. In Italy they wouldn't get the chance. The only problem with the large porcini is that they are darker when dried so it is better to pick them small as they remain light and don't colour the risotto too much.
Once they have been picked they need to be cleaned and sliced.
The slices are about 1cm thick. They have to be this thick as they are nearly all water and if you cut them too thin they will be so papery that they will crumble to nothing.
To dry them you will need warm Italian sunshine, or failing that a fan assisted oven with a low temperature of 50C. Lay them out on the rungs of the oven trays and wedge the door open slightly. I use a wooden spatula. the aim is to keep the temperature low and not to cook the mushrooms. After about 12 hours like this the porcini should be dry. If you feel them damp in any way leave them longer. they must be bone dry to keep. They should be stored in an air tight jar or they will absorb moisture and go off quickly.