See Perfect Egg Whites
For the meringues place the egg whites in a large clean bowl and whisk them until they form stiff peaks (it's very important, though, not to over-whisk the egg whites because, if you do, they will start to collapse).
Now start to whisk in the sugar, about a tablespoon at a time, whisking after each addition until all the sugar is in. Now all you do is spoon 8 heaped dessertspoons of the mixture on to the prepared baking sheet, spacing them evenly.
Then, using the back of the spoon or a small palette knife, hollow out the centres. Don't worry if they are not all the same shape – random and rocky is how I would describe them.
Next, pop them on the centre shelf of the oven and leave them for 30 minutes. After that, turn the oven off and leave the meringues to dry out in the warmth of the oven until it is completely cold (usually about 4 hours).
While the meringues are cooking you can make the lemon curd: place the grated lemon zest and sugar in a bowl, whisk the lemon juice together with the eggs, and pour this over the sugar. Next add the butter cut into small pieces, and place the bowl over a pan of barely simmering water (making sure the bowl does not touch the water).
Whisk every now and then until thickened, which should take about 20 minutes. Then leave it on one side to cool.
When your ready to serve the meringues (or up to 20 minutes ahead) whisk the filling ingredients together.
Spoon a small blob of filling onto each plate and top with a meringue (this will help the meringues stay in place). Then divide the lemon curd amongst the meringues and top each one with a generous blob of the filling.
Finish with a dusting of icing sugar.