Pre-heat the oven to 120C.
Chop off the top and bottom of the pears.
Thinly slice (about 1mm thick) as uniformly as possible.
Lay out the pear slices on a baking tray ensuring that none of the slices are overlapping and place in the oven for 1 hour 15 minutes.
After 1 hour 15 minutes, turn the pears and return them to the oven for a further 1 hour 15 minutes.
After they have finished cooking, turn off the oven but leave them in the oven for a further hour to become fully crisp.