Heat a high sided skillet over medium heat. Sprinkle bottom with salt and heat for one minute to create a non-stick effect. Add oil or stock and heat for 30 seconds.
Add onions and cook until translucent, about 5 minutes. Add cabbage, stir in and let wilt slightly, about 3-4 minutes. Add apple and a pinch of salt, stir to combine.
Add mustard, ground mustard, tahini and apple cider vinegar. Mix in. When thoroughly mixed, add stock and and pinch of salt. Bring to a boil. When boiling, reduce to a simmer and cook covered for about 15 minutes.
Remove cover and continue to cook, stirring occasionally until liquid is reduced to almost nothing and cabbage is very soft.