If you are using homemade meringues, make these first. Preheat your oven to 110C/100C Fan/Gas ¼ and line a baking sheet with non-stick baking paper.
Put the egg whites into a clean mixing bowl and beat with an electric whisk until stiff peaks form when you lift out the whisk. Whisk in the caster sugar, one tablespoon at a time, until the mixture is really thick, glossy and will hold in a stiff peak. Briefly whisk in the vanilla.
Place 5 large dollops of the meringue on the prepared baking sheet, leaving space in between. Bake on the lowest shelf of your oven for an hour, or until the meringues easily peel away from the paper. Cool and keep in an airtight container for up to 3 days before using.
For the mess, put 150g/5½oz of the strawberries into a blender or food processor with ½ tablespoon of the icing sugar. Pulse to form a smooth purée. Halve or quarter the remaining strawberries into bite-size pieces.
Whip the double cream and remaining 1½ tablespoon of icing sugar together until soft peaks form when you remove the whisk (they should almost hold their shape).
To assemble, crumble 4 of the meringues and add to the cream along with all the berries. Fold in lightly, then very briefly stir in the strawberry purée to make swirls in the cream (as you spoon the mess into bowls it will ripple more). Divide between 6 bowls or glasses, crush the final meringue over the top and eat immediately.