For the creamed potato, place the potatoes into a saucepan and cover with water. Add a pinch of salt, bring to the boil, reduce the heat and simmer for 10-12 minutes until tender.
Drain and return to the pan. Place the pan over the heat to remove any excess moisture.
Pass the potatoes through a potato ricer until smooth (or use a potato masher, though you will not get such a smooth result) and return the mash to the pan.
Add the cream and butter and beat well. Season, to taste, with salt and freshly ground black pepper and set aside, keeping the mash warm.
For the fish and spinach, season the sole fillets with salt and freshly ground black pepper.
Heat a frying pan until hot, add half of the butter and the sole fillets. Fry for two minutes, then turn the fish and add the mushrooms and the remaining butter to the pan. Cook for a further 2-3 minutes, or until the mushrooms are golden-brown.
Remove the fillets from the pan and pat dry briefly on a piece of kitchen towel. Set the mushrooms aside.
Meanwhile, heat a separate frying pan until hot, add the remaining butter and the spinach and cook until just wilted. Set aside, keeping it warm.
For the sauce, heat a frying pan until hot, add one-third of the butter and all of the shallots. Cook for 1-2 minutes or until the shallots have softened, but not browned.
Add the peppercorns and Chinese five spice powder to the shallots and cook for a further minute.
Add the sherry vinegar and stir until it has absorbed into the shallots. Add the red wine, fish stock, bay leaf and thyme, bring to the boil, then reduce the heat and simmer until the mixture has reduced in volume by two-thirds.
Strain the sauce through a fine sieve into a clean saucepan and whisk in the remaining butter and the lemon juice. Season with salt and freshly ground black pepper, to taste.
To serve, spoon the creamed potato onto the centre of each of two serving plates and pile the spinach alongside. Lay the fish fillets on top, scatter over the mushrooms and spoon around the sauce.