Lemon mousse

Soften the gelatin in cold water. Wash the limes, grate them to obtain the zest, squeeze them, and strain the juice.
Squeeze the lemons and reserve the juice.
Crack the eggs, separating the whites from the yolks. Whisk the yolks with the sugar in a bain-marie until the mixture whitens. Pour in the crème fraîche and whisk over low heat until thickened for 7 to 8 minutes. Remove from heat and let cool.
Heat the zest with the lemon juice and melt the gelatin. Gently pour into the egg custard while mixing.
Beat the egg whites until stiff and gently fold them into the previous mixture. Pour into individual molds and let set for 6 hours in the refrigerator.
When ready to serve, dip the molds in hot water for a few seconds and turn them out onto plates. Serve chilled.