or trout*, cold cooked
*Note: Salmon, sea trout or river trout may be used (farmed trout is unsuitable - its texture is too soft).
Peel and seed the cucumber and cut the flesh into pieces no larger than matchsticks.
Sprinkle with ½ teaspoon each salt and caster sugar and 1 teaspoon tarragon vinegar.
Toss lightly and set aside for at least 40 minutes, or all day if you prefer, to draw out some of the cucumber juices.
Drain well and pat dry.
Cook the rice in double its volume of boiling salted water or, better still, in fish stock.
It will take about 35 minutes to become tender.
Towards the end of this time cook the vegetables.
Boil the peas in a little lightly sugared water.
Melt the butter in a flameproof casserole, add the sticks of cucumber and cook over medium-low heat for 2 minutes, just stirring occasionally.
Break the skinned and boned fish into big flaky chunks.
Lay the fish on top of the cucumber - don't stir it in.
Cover the casserole and reduce heat as low as possible.
Leave to cook, just shaking the casserole occasionally, until the cucumber is tender and the fish is well heated through - 4 minutes or so.
Meanwhile put the watercress into a food-processor and reduce it to green flecks.
To assemble the kedgeree, add the prepared watercress, peas and cooked rice to the buttery fish and cucumber mixture.
Immediately draw the casserole away from the heat and season it generously with sea salt and freshly ground black pepper.
Toss the ingredients gently but thoroughly to mix them well and serve straight away with a large fresh green salad, or with a tomato salad if you prefer