Preheat the oven to 110C/90C Fan/Gas ¼.
For the cabbage, pick off the green outer leaves and cut the stems off them. Cover and put in the fridge. Slice the rest of the cabbage into 1cm/½in strips and mix with the oil. Spread them out on a baking tray and dry in the oven for 12 hours. Keep the oven door ajar by 2.5cm/1inch.
For the pickled onions, heat the vinegar and sugar with 4 tablespoons water and 1 teaspoon salt in a saucepan over a medium heat. Put the red onions in a bowl, pour over the pickling liquid and leave to cool.
Blanch the green outer cabbage leaves in salted water for 1–2 minutes. Plunge into iced water and drain. Set aside.
For the creamed barley, bring the stock to a simmer. Melt the butter in a saucepan over a medium heat and sauté the shallot and garlic until softened but not coloured. Add the barley and sauté for 3–4 minutes, stirring constantly. Add the wine and simmer, stirring, until the liquid has been absorbed.
Add a ladleful of the stock and simmer, stirring again, until the liquid has been absorbed. Continue adding the stock in this way, until all the liquid has been absorbed and the barley is plump and tender. This should take about 15 minutes. Add the cheeses and stir until you have a smooth consistency. Season with salt.
Julienne the beetroot into matchsticks using a spiraliser or mandolin and season with salt. Slice the fennel thinly using a mandolin and rinse under cold water.
For the salmon, toast the spices in a dry frying pan over a medium heat until fragrant (keep an eye on them, you don’t want them burn). Blend in a spice grinder until you have a fine powder. Season the salmon with salt and coat in the spice powder. Heat a frying pan over a high heat and sear the salmon fillet for 10 seconds on each side. Allow to rest for a couple minutes before slicing into 25.cm/1in pieces.
Serve the creamed barley topped with the seared salmon, blanched cabbage, dried cabbage, pickled onions, beetroot noodles, crispy fennel, freshly grated horseradish and buttermilk, (if using).