Halve the lemons and slice as thinly as you can - you can use a food processor blade or a mandolin.
Remove any pips you come across.
Place the slices in a bowl and sprinkle with the salt and chilli flakes.
Allow to sit for 30 minutes at room temperature.
Mix again, then push the lemon slices into a sterilised jar so that they are tightly packed with all the liquid that accumulated in the bowl.
Cover with olive oil and seal the jar. These will be ready to use the next day, but will improve with time.
Once opened, store in the fridge and use within a month.
When you come to cook with them,just take as much as you need for the recipe.
Chop and use the entire slice - you don't have to discard the flesh as you do for whole preserved lemons. The slices can be eaten as a relish with fish or chicken dishes, and you also use them mixed with mayonnaise and harissa to accompany a great chicken or tuna sandwich.