Peel the onion and cut in half once. Use the kitchen slicer to slice the onion halves into wedges or half rings. You can of course do this with a sharp knife. But with the plane they become so nice and even. Put the flour in a bowl and roll the onions in it until they are really nice and floury.
Heat the fat in a saucepan (of course you can also use the deep fryer) and add the onions. Let sizzle for about 5 minutes until they are golden brown. Put a pair of tongs or a slotted spoon in a sieve and let drain briefly and you`re done!