If using fresh chestnuts, you have to roast them. Preheat the oven to 350°F/170°C. Using a sharp knife, make a slit on the rounded side of each chestnut. Spread the chestnuts in a single layer in a baking pan and bake for 30 minutes, or until the skins crack and curl a little. Remove the chestnuts from the oven. While they are still warm, remove the hard outer shells and the fuzzy inner skins
If using sous vide chestnuts, place the bags in boiling water for five minutes. Remove, cool slightly, open and transfer the chestnuts to a saucepan.
In a saucepan over low heat, combine the raki or ouzo, salt, and sugar and stir to dissolve the sugar. Be careful not to heat on too high a flame, lest the raki or ouzo ignite. Add the chestnuts and cook until the liquid is reduced to a thick syrup, about 30 minutes. Transfer the chestnuts to a serving dish and serve hot.