When it comes to cleaning, the classic way is to cut the base, then remove the leaves from around the endive, until you have a very clean vegetable. Classic, but not great, the loss is important, especially if the endive comes from the sand, you have to remove a lot of leaves (too many), to have one ready to be used in a recipe.
Can we do better?Yes, it is better to wash it in fact, before trimming it, but this washing should not be done like for another vegetable, by soaking them in water for example. On the contrary, on the one hand they get waterlogged if you do that, but on the other hand a small part of the sand that was on the turn will end up in the endive, and when tasted it will crunch under the tooth very unpleasantly.
No, here's the thing, in fact it's better to proceed like this: Run a trickle of warm water from the tap, and put the endive underneath one by one, with the head down, like this:
This way, the sand goes into the sink, the endive does not get waterlogged, and the peeling after drying with a cloth, will consist in removing 1 or 2 leaves from the turn, not more, or even none.
You will note that on the photographs they are red endives, with the season alas even shorter, but which are less bitter than the yellow ones, and of a superb esthetics which make it possible, inter alia, to make a little of decoration in your receipts/plates at little expenses.
One last point about the plastic endive from the supermarket, you have probably noticed that they are absolutely clean, not a grain of sand or dirt. Is it normal knowing that it comes from the earth or sand? To look like this on the shelves, you have to imagine that they must have received a shock treatment, probably not neutral, which have scoured them, or even more. In short, trust your local grower who plants locally.
To sum up: Wash your endives under a trickle of warm water, upside down, before drying them and
trimming them.