Preheat the oven to the lowest setting and line trays with paper marked with 5cm circles.
Whisk egg whites and lemon juice to soft peaks, then gradually whisk in the caster sugar to stiff peaks.
Pipe the meringue into nests onto the prepared trays using a star nozzle.
Bake for 90 to 120 minutes until they lift easily, then cool on a wire rack.
Whisk the second set of egg whites to stiff peaks and whisk double cream with icing sugar in a separate bowl.
Blend strawberries in a processor and pass through a fine sieve.
Dissolve gelatine in 60ml of puree over low heat, mix with remaining puree, then fold into cream and egg whites.
Chill the mousse, then pipe into nests and top with a strawberry half.