Inspired from: Après la saucisse aux choux, voici le papet Vaudois! and several others and in particular:Hard-Boiled Swiss Jesus (Boutefas).
Comment: Specialty of the canton of Vaud, it is the typical accompaniment to cabbage sausages or "saucissons".
Washing the leeks is very important, because they have a good habit of hiding a little soil. Simply, remove the green part which is washed separately, then cut the top of the trunk in cross or in half and wash with running water by orienting the leek downwards so that the soil does not seep further down the leek.
As you must certainly add liquid during cooking, use 1 or 2 ladles of the sausage water (or cabbage sausages).
Finally, the sausage or cabbage sausages should not normally be pierced. Cook them at 70C (160F), the "saucisson" for 60 to 75 minutes, the cabbage sausages for 30 minutes.
Some recipes recommend adding a little good vinegar at the end, to enhance the taste of the leeks. I tried without and with, I think it's a good idea. Use a good white wine vinegar.
Potatoes: normally one would use half as much as leeks in weight, I prefer less (1/4).
~1.2 kg leeks (6 to 8 leeks)
300 g potatoes
3 dl white wine (don't be afraid to put too much!)
2 tablespoons of good white vinegar (opt)
Butter or EVOO
Wash the leeks and cut them into large pieces of 2 to 3 cm, split the largest leeks in half beforehand.
Peel the potatoes and cut them into cubes of ~1 cm.
Sweat the leeks in enough butter or EVOO and a little salt (7 to 10 minutes).
Deglaze with white wine.
Add the potatoes, check the salt, cover and cook ~45 to 60 minutes until the potatoes are cooked through.
Add a little water (or better sausage cooking water) during cooking (likely as early as when the wine has reduced).
Check the salt, one or 2 knobs of butter, 2 tablespoons of vinegar, stir well and mash the potatoes a little before serving.