Duck sous vide:
Cook the sugar, salt, and spices in one litre of water and let the marinade cool down.
Thoroughly clean and wash the duck and soak it in the chilled marinade for 3 hours. Thoroughly dry the duck with kitchen towels. Vacuum seal it in a suitably large plastic bag. Cook in the Gorenje sous vide cooker for approximately 4 hours at 63 °C.
Before serving, crisply brown the duck on both sides under the broiler.
Sauté the roughly chopped onions and apple over oil. Add Port wine and cook until all liquid evaporates. Add duck stock and reduce to one half. Season with salt, pepper, and a pinch of sugar. Strain the sauce through a fine-mesh sieve and add the starch. Finally, add coarsely chopped tarragon.
Caramelize the butter and sugar in a skillet. Add the chestnuts and glaze for a few minutes. Add water, season with salt, and cook for 10 to 15 minutes on low heat.
Clean the Savoy cabbage and remove the outer leaves. Quarter the Savoy cabbage head, remove the stalk, and separate into leaves. Roughly chop the leaves, blanch them for 3–4 minutes in boiling salted water, and chill in ice water. Strain well and press firmly with your hands. Finely chop the Savoy cabbage in Gorenje Chef's Collection food processor.
Make oignon piqué (place the bay leaf over the onion and pierce it with a clove). In a skillet, dissolve butter, add the flour, and cook until the mixture turns a light golden colour. Add cold milk and the oignon piqué, and cook slowly for 20 minutes. Strain the Béchamel sauce through a fine-mesh sieve and season with salt.
Lightly sauté the finely chopped bacon and shallot over butter. Add chopped Savoy cabbage, season with salt, pepper, and nutmeg, and cook slowly on medium heat for 4 to 6 minutes. Just before serving, add 100 ml of the Béchamel sauce.