1 Preheat an oven to 170 degrees (fan oven), or equivalent. Grease and line a 30cm by 20cm baking tin with baking parchment (cut the paper higher than the sides of the tin so the meringue doesn't catch when it rises).
2 Put the egg whites and salt into a large mixing bowl and use an electric whisk to whisk to soft peaks. Gradually add the sugar in spoonfuls, continuing to whisk on a high speed for at least 5 minutes, until the mixture is glossy and forms stiff peaks.
3 Using a spatula, spread the mixture into the lined tin and bake for 15 minutes (then turn down the heat to 160 degrees and bake for another 5 minutes) until the surface is pale golden and firm (don't overcook it or it may crack). Remove from the oven and leave to cool completely.
4 For the lemon curd: Melt the butter in a medium-sized heavy based saucepan on a low heat. Add the sugar and lemon zest and juice. Stir until blended. Remove the pan from the heat and slowly pour the buttery liquid on to the egg yolks in a bowl, whisking to incorporate. Return the egg yolk and lemon mixture to a clean saucepan and place on a low heat, stirring constantly until the mixture thickens slightly. When the mixture coats the back of a spoon, remove it from the heat and transfer the curd to a clean bowl, allowing it to cool slightly before refrigerating it for 1-2 hours (it will thicken as it chills).
5 Once the roulade has been baked and the lemon curd has been chilled you are ready to assemble and roll the roulade. Place a sheet of baking parchment wider than the baking tray on to a flat surface and lightly dust with icing sugar. Rest the long edge of the tin on the work surface and invert the baked meringue on to the dusted paper, remove the tin and carefully peel back the lining paper.
6 Spread half the lemon curd on to the surface of the meringue. Fold the remaining lemon curd through the whipped cream. Spread the lemon cream over the surface of the roulade.
7 Positioning the short edge in front of you, roll the roulade upwards and away from you using the paper to help roll over like a swiss roll.