01 - Combine chopped dates with water in a small saucepan. Cook over medium heat for 5-7 minutes until dates soften and mixture forms a thick paste. Stir in orange blossom water and lemon juice. Let cool completely.
02 - Whip chilled heavy cream in a mixing bowl until soft peaks form. Refrigerate until ready to use.
03 - Beat egg yolks with half the sugar and vanilla extract in a separate bowl until mixture becomes pale and thick.
04 - Whisk egg whites with pinch of salt in a clean bowl until foamy. Gradually add remaining sugar and continue beating until stiff peaks form.
05 - Gently fold cooled date paste into egg yolk mixture until thoroughly incorporated.
06 - Fold whipped cream into date-yolk mixture. Gently fold in egg whites until mousse is smooth and airy.
07 - Spoon mousse into individual serving glasses. Refrigerate for at least 2 hours until set.
08 - Top with chopped pistachios, orange zest, and dried rose petals if desired before serving.