Into the bowl of your Kenwood chef kitchen machine, fitted with the balloon whisk, add the egg whites and set the speed to 6 until they form soft peaks.
Slowly begin adding the caster sugar, one spoonful at a time. Once incorporated, continue whisking the meringue for another couple of minutes.
Whilst the machine is whisking the egg whites, in a small bowl, stir together the white wine vinegar, cornflour and 1tsp of the vanilla extract.
Once you have a stiff glossy meringue, turn off the machine and remove the bowl. Gently fold in the vinegar, cornflour and extract mixture until just combined.
Line your baking sheet. A touch of meringue at each corner of the baking sheet can help to secure the parchment on top. Spread the meringue mixture evenly onto the baking sheet.
Bake the meringue in the preheated oven for 30-40 minutes, until it is risen, and slightly golden.
Remove the meringue from the oven, and lightly dust with caster sugar. Carefully turn the meringue out onto a clean tea towel and remove the parchment. Leave to cool for no longer than 10 minutes.
Whilst the meringue is cooling, prepare the filling. Into the clean bowl of your kitchen machine, fitted with the balloon whisk, add the double cream and remaining tsp of vanilla extract. Whisk until thickened.
With the meringue on the counter in front of you, landscape style, spread the cream over the near half of the meringue, reserving 6tbsp to top the roulade. Spoon over 4tbsp of lemon curd, and swirl into the cream gently.
Using the tea towel to assist you, carefully roll the roulade away from you. Transfer to a serving dish, and top with the remaining cream and lemon curd, swirling together.