Place the chopping board on a damp cloth. Remove any loose papery skin from the onion to stop your knife from slipping when making the first cut.
Cut off the root end of the onion.
Stand the onion on the cut root end and slice the onion in half downwards from stalk to root end.
Take one onion half and carefully peel away the papery outside layers.
Now cut off the stalk end.
Turn the onion so one of the cut ends is facing you. Hold the onion with your fingers curled under and use your second finger knuckle to guide the blade. Slice from one cut end to the other, at the required thickness.
notes
Always put a damp cloth under the chopping board to prevent it from slipping.