01 - Combine chopped dates and 2 tbsp water in a small saucepan. Cook over low heat for 3-4 minutes, stirring constantly until soft and jammy. Remove from heat and let cool to room temperature.
02 - In a large bowl, whip the cold heavy cream to soft peaks using an electric mixer or whisk. Place in refrigerator to keep cold until needed.
03 - Whisk egg yolks with granulated sugar in a separate bowl until pale and thick, about 3 minutes. Stir in orange blossom water and lemon zest until combined.
04 - Transfer cooled date mixture to a food processor or blender. Process until smooth paste forms. Fold date paste into egg yolk mixture until fully incorporated.
05 - Gently fold the chilled whipped cream into the date-yolk mixture in two additions, using a spatula with light lifting motions until smooth and airy.
06 - In a clean bowl, whisk egg whites to stiff peaks. Carefully fold into the mousse base using gentle folding motions, maintaining as much air as possible.
07 - Spoon the mousse into individual serving glasses or bowls, filling each about three-quarters full. Smooth tops with a spatula.
08 - Refrigerate for at least 2 hours or until completely set and firm to the touch.
09 - Top with chopped pistachios, finely grated orange zest, and sliced dates before serving.