"Chicons au gratin" is mainly known in my own country but you will find it in many bistros in France too, maybe under the same name or as "endives au gratin". This dish is something you would get served in a household on a cold wintery weekday. If you don't find endives, you can use the white part of leeks instead, also quite delicious!
Start with preparing the endives. Cut a little piece of the core out of the root end. Might be too bitter. Now you can simply boil the whole endives in salted water for around 20 minutes (they have to be soft, not crunchy al dente, punch with the tip of a knife to test). Take them out of the water and let the water drip out. This is what most people do.
Another more "cheffy" way of preparing them is to braise them. That's what I did (I'm retired, I have plenty spare time) as the flavor result is probably x10 compared to boiled ones. Simply fry the whole endives first in butter to get a little color, season with s&p and nutmegg. Then add a bottom of water, cover with a "cartouche" or simply said a round of parchement paper and let braise for 45 minutes on low fire. They come out all soft and caramelized as in the pictures below.
You also need a bechamel sauce. Melt some butter, add equal part plain flour, let fry gently for a few minutes while stirring, then add cold milk a bit at a time and whisk well all the time. Keep adding milk untill you reach the consistency you prefer. s&p &nutmegg.
Preparation with smoked salmon
Make a bechamel sauce, add a tbsp of mascarpone (your doctor's wallet will love you for using too much mascarpone &C°, it's 80% fat...).
Roll a cooked endive in a piece of smoked salmon. Put all rolls in an oventray, cover with the sauce. Sprinkle some panko or other breadcrumbs over the preparation and put some small pieces of butter on them. Put in the oven to heat through, at the last moment put the ovengrill on and let the top color.
Classic version of chicons au gratin (=always using ham)
Make a bechamel sauce again but turn it into a Mornay sauce simply by adding grated cheese (I used both Comté and Gruyère). Roll in a piece of ham. Cover the rolls with the sauce. Spread some grated cheese on top. Same oven treatment as above.