Pre-heat the oven to gas mark 5, 375°F (190°C).
First of all make up the hollandaise: put the butter into a small saucepan and allow it to melt slowly. Place the wine vinegar and lemon juice in another pan and bring these to the boil. Meanwhile blend the egg yolks in a liquidiser or food processor with a pinch of salt, then – with the motor still switched on – gradually add the hot lemon and vinegar. When the butter reaches the boil, start to pour this in very slowly in a thin trickle (with the motor running all the time) till it is all added and the sauce is thickened. Pour it into a small bowl and stir in the snipped chives. Cover the bowl with clingfilm and leave in the fridge until the sauce is cold and set.
Next, scrub the potatoes thoroughly and dry them with a tea towel, then leave them aside for the skins to dry completely (if you get ready-scrubbed potatoes, just wipe them with damp kitchen paper). When the skins are nice and dry, prick them with a fork, then moisten your hands with oil and rub the potatoes to oil them all over. Put about 1 tablespoon Maldon salt in a bowl and swirl each potato in the salt to coat it lightly.
Place the potatoes on a baking sheet and bake for 1 hour, or until crisp and tender. Then, when you're ready to serve, cut a cross in the top of each potato and gently squeeze up from the base to open out the cut slightly (use a tea towel to protect your hands). Arrange the potatoes together on a large warmed serving dish and quickly top each one with a spoonful of the chive hollandaise (or any of the other toppings mentioned above).