Preheat the oven to 160C/325F/Gas 3. Lay a piece of baking paper on a baking tray and draw a 25cm/10in circle on it.
Put the egg whites into a bowl and whisk on the fastest speed with an electric hand-whisk or in a free-standing mixer until stiff. Gradually, still whisking on maximum speed, add generous teaspoons of sugar until the mixture is stiff and shiny and stands in peaks.
Blend the vinegar and cornflour together in a cup and mix until smooth. Stir this into the meringue mixture.
Spread half of the meringue mixture onto the paper to give a 25cm/10in circle. Fill a piping bag, fitted with a rose nozzle, with the rest of the meringue mixture. Carefully pipe about 10 separate little nests positioned equally around the edge of the circle.
Slide the meringue into the middle of the oven, turn the heat down to 150C/300F/Gas 2 and bake for 1½-2 hours (check after one hour), or until it easily comes off the paper. The pavlova will be a pale creamy colour rather than white. Turn off the oven and leave the pavlova in the oven to become cold.
Meanwhile, make the lemon curd for the filling. Place a heatproof bowl over a pan of hot water, simmering gently on the stove. Add the egg yolks, sugar and lemon juice to the bowl and whisk. Gradually add the butter, whisking continually until it starts to thicken. It should coat the back of a spoon when it reaches the correct consistency. It will firm up further once cooled.
Whisk the double cream in a large bowl until thickened, then swirl it through the cooled lemon curd.
Spoon the lemon curd and cream mixture into the middle of the pavlova and spread over the base of the meringue nest. Spoon a lemon filling into each of the mini nests. Decorate by placing three chocolate mini-eggs in each of the 10 mini-nests around the edge of the dessert.
Put 100ml/3½fl oz water and the caster sugar in a pan. Bring to the boil, stirring. Add the zest and boil for 2-3 minutes, or until syrupy. Drain on parchment paper, roll in extra caster sugar and leave to dry in a warm place for a couple of hours, or overnight. Place a delicate mound of candied zest in the middle of the pavlova, and serve.