For the hollandaise sauce, in a pan, heat the vinegar, peppercorns, bay leaf, tarragon and 50ml/2fl oz water and cook until the liquid has reduced in volume to a tablespoon. Strain through a sieve.
Put the liquid and the egg yolks in a food processor and blend. With the motor running, gradually add the clarified butter until you have a smooth sauce. Finish with the lemon juice, mustard and cayenne pepper. Set aside and keep warm (cover the mixture to prevent a skin from forming on the surface).
For the smoked salmon hash brown, place the potato, salmon, smoked salmon, crème fraîche and dill in a large bowl and mix. Heat a large frying pan until hot and add the butter.
To make each hash brown, place a metal ring in the centre of the pan and pack it with the mixture. Cook for 2-3 minutes on each side until golden-brown and crisp.
For the poached eggs, bring a pan of salted water to the boil and add the vinegar. Reduce the heat to a simmer and whisk the water to create a whirlpool. Once settled, crack an egg in. Simmer for 2-3 minutes, remove the poached egg carefully with a slotted spoon and place on a plate to drain. Repeat the process with the remaining eggs.
To serve, place the salmon hash in the centre of serving plates and top with the egg and hollandaise sauce. Just before serving break the egg yolks.
You don't need a chefs' ring to make this potato cake, but it does help it to hold together better when you flip it over. If you don't mind a bit of falling apart, then you can go without it. Shop-bought hollandaise is also acceptable if you can find a good one.