For the meringues, preheat the oven to 180C/160C Fan/Gas 4. Line a large baking sheet with non-stick baking paper or a silicone mat.
Whisk the egg whites in a clean, glass bowl using an electric hand whisk until stiff peaks form when the whisk is lifted out. Gradually add the sugar, one spoonful at a time, and whisk well between each addition. Whisk until very stiff and glossy and all the sugar has been added.
Spoon the mixture onto the lined baking sheet, creating a 35x25cm/14x10in rectangle, and smooth the surface. Sprinkle with most of the lemon verbena. Bake for 8 minutes, or until golden brown. Reduce the temperature to 170C/Fan 150C/Gas 3 and bake for a further 12 minutes, or until crisp.
Lightly dust a sheet of baking paper with caster sugar. Allow the meringue to cool slightly before turning it out onto the baking paper, lemon verbena side down. Leave to cool.
For the filling, put 200g/7oz strawberries in a blender and blend until smooth. Pass the mixture through a sieve into a bowl to remove the seeds.
Lightly whisk the cream in a large bowl. Stir in the strawberry sauce and 100g/3½oz of the remaining strawberries. Spread the strawberry cream evenly over the meringue. Starting at the long end, roll the roulade up using the paper to help you.
Decorate the top of the roulade with the remaining strawberries and lemon verbena leaves and dust with the icing sugar.