- Peel the cucumber and slice into 1mm using a mandolin or a very sharp knife. Put in a container with a lid, adding the vinegar and salt. Close with lid, shake and let the cucumbers marinate for half an hour, then drain.
- Arrange the bread slices as an even layer. Spread the mayonnaise on all slices, then cover four with cucumber slices and then a generous pile of watercress or rocket. Finish with grating half of the Le Gruyère AOP on them.
- Press the remaining four slices of bread to form four sandwiches and arrange them on a square tray or medium cutting board covered with a piece of parchment or cooking paper. Place another piece of paper on top, then wrap the tray and sandwiches firmly with cling film, making sure no air gets in. Place another tray or cutting board ontop to press the sandwiches lightly and put in the fridge to rest for at least 4 hours, preferably over night. -If the top tray or cutting board is very light, you can weigh it down with something, just make sure not to squish the sandwiches or press them unevenly.
- After the sandwiches have set, unwrap them and cut off the rinds of the bread, then slice each diagonally. To granish, grate the rest of the cheese finely onto a small plate, generously butter one side of each sandwich and press into the cheese to make a beautiful, cheesy rind for each afternoon sandwich. Serve straight away.
Preferably prepare the sandwiches the previous night, so they have time to set in the fridge and absorb the good flavours fot he cucumber and mayonnaise.
