Wash and hull the strawberries to make the mousse. Pour them into the bowl of the mixer then mix to obtain a coulis.
In a saucepan, heat the strawberry coulis, powdered sugar and lemon over medium heat for about 8 minutes.
Off the heat, melt the drained gelatin and mix. Let cool to room temperature.
Whisk the egg whites then add the cooled strawberry coulis. Whisk to incorporate well.
Whip the cream until stiff. Using a spatula, fold the whipped cream into the strawberry mixture.
Cut the strawberries for the decoration in half and place in the bottom of the glasses, against the wall. Distribute the strawberry mousse among the glasses (using a piping bag or a spoon).
Refrigerate for at least 4 hours, overnight is better. Optionally, add half a strawberry on top for decoration.