For the omelette, pour the milk into a large shallow pan. Add the smoked haddock, smoked salmon, bay leaf and peppercorns. Bring to a simmer. Cook for five minutes, or until the fish has just cooked through and flakes when pushed gently. Lift the fish out of the pan and set aside to cool slightly before gently flaking, discarding the skin. Strain the milk into a clean pan.
Heat a frying pan until medium-hot, add 1 tablespoon of the butter and the eggs. Cook gently, stirring with a fork until they just hold together.
Add half the flaked fish to the top of the omelette. Roll out of the pan onto an ovenproof serving dish and top with the remaining fish.
Preheat the grill to hot.
Clean the omelette pan with kitchen paper, return to the heat and melt the remaining butter. Add the flour and cook stirring well for two minutes. Gradually add the reserved milk, whisking all the time until it forms a smooth sauce. Season with salt and pepper. Pour the sauce over the top of the omelette and scatter with the cheese. Place under the grill for 3-5 minutes, or until golden-brown and bubbling.
Meanwhile for the salad, mix all of the salad ingredients together in a large salad bowl.
For the dressing, combine all of the dressing ingredients in a blender until smooth. Just before serving, pour some of the dressing over the salad and toss. Any leftover dressing can be kept in the fridge for a few days.
To serve, put the omelette in the centre of the table and place the dressed salad alongside.