Put the egg white into a heatproof bowl with the icing sugar. Set the bowl over a large pan of simmering water and, using a hand electric whisk, whisk for 5 mins until the mixture is light, fluffy and holds peaks when the blades are lifted.
Remove from heat, whisk in the lemon zest, then whisk for a further 2 mins to cool it down.
Fold in the fromage frais, then transfer to six glasses or small bowls and chill. Roughly chop half the strawberries and put in the food processor with the 2 tbsp icing sugar and the lemon juice. Whizz to a pure, then press through a sieve to remove the seeds. Chop the remaining strawberries.
Spoon the chopped strawberries over the mousses, then spoon a little pure over each. Chill until ready to serve.
