First, prepare the fish for smoking. Put the pieces of salmon, skin side down, on a plate or tray and sprinkle with two tablespoons of the light brown sugar (keep the remaining one tablespoon for smoking the salmon) and the salt. Allow the fillets to sit somewhere cool in the kitchen for 30 minutes.
When the salmon fillets have been sitting for half an hour, pat them dry with kitchen paper then leave them, uncovered, for another half an hour to dry out slightly. Sprinkle the remaining tablespoon of light brown sugar, the uncooked rice, the tea leaves and the wood shavings in the base of your smoking box, biscuit tin or wok, whichever you’re using, then place a wire rack inside.
Next, make the horseradish sauce. Put the grated horseradish into a bowl with the white wine vinegar, the lemon juice, the Dijon mustard, the salt and the freshly ground black pepper and the sugar. Fold in the softly whipped cream, but do not over-mix the sauce or it will curdle. The sauce will keep in the fridge for five to six days.
Put the salmon pieces, skin-side down, in a single layer on the rack of your smoking box, biscuit tin or wok, whichever you’re using. Turn on the heat to high (this can be done on a gas or electric hob, or on a stove or Aga) and once the wood shavings are smoking, turn the heat to low and cover the smoking box, tin or wok with a tight-fitting lid or one made of tinfoil, and cook for eight minutes. Then, take the smoking box, biscuit tin or wok off the heat and, still covered, allow it to sit for another four minutes. When it is ready, the fish should look cooked in the centre.
Transfer the warm salmon to plates and serve it with the horseradish sauce and hot boiled new potatoes.