Firstly take some raffia and make a loop like so with a short length just longer than the stalk on the right,and the other end with about 2 feet of raffia to tie on the left.
Then keeping the loop in position with your thumb wrap the other end of the raffia around the dryest section of the neck as tightly as you dare.
Continue to do this going up and down the neck until you finish at the bottom with a few inches of raffia left.
Then pass the spare raffia through the loop like so and carefully pull the other end of the raffia slowly upwards to draw the loop up towards your tied neck.
Then when you have pulled the end to draw the loop up so it is just under the tied neck ,stop.
Cut the spare raffia off and then pull the other end just slightly to hide the cut end.
Then cut the excess raffia from the top and trim the top of the onion if you have a lot sticking out.
So that's about it,you can do the same with smaller onions and shallots too.
Here's the same thing in Video.