Soak gelatine in cold water. Wash the untreated lemon and grate the rind finely. Squeeze all lemons. Mix juice, lemon peel and buttermilk. Season to taste with sugar
Squeeze the gelatine and dissolve at low heat. First mix with some lemon butter milk, then stir into the rest. Chill the mixture until it begins to gel
Whip cream until stiff and fold in. Pour the lemon mousse into glasses and chill for at least 4 hours
Roast the almonds without fat until golden brown. Take out and let cool down. Sprinkle the mousse with almonds. Decorate with melissa and dust with icing sugar