01 - Combine chopped dates and 2 tbsp water in a small saucepan. Cook over low heat for 3-4 minutes, stirring frequently until dates break down into a soft, jammy consistency. Remove from heat and let cool completely to room temperature.
02 - In a chilled mixing bowl, whip cold heavy cream using an electric mixer or whisk until soft peaks form. Refrigerate immediately to maintain structure.
03 - Whisk egg yolks and granulated sugar in a separate bowl until mixture becomes pale yellow and thickened, approximately 2-3 minutes. Incorporate orange blossom water and fresh lemon zest until fully blended.
04 - Transfer cooled date mixture to a food processor or blender. Process until completely smooth and uniform, then fold into the egg yolk mixture until no streaks remain.
05 - Gently fold one-third of the refrigerated whipped cream into the date-yolk base to lighten the mixture. Add remaining cream in two additions, folding with a spatula using gentle, lifting motions to preserve airiness.
06 - Using a completely clean bowl and beaters, whip egg whites until stiff glossy peaks form. Fold whites carefully into the mousse base in two batches, maintaining maximum volume.
07 - Distribute mousse evenly among individual serving glasses or bowls. Refrigerate for minimum 2 hours or until completely set and firm to the touch.
08 - Just before serving, top each portion with chopped pistachios, finely grated orange zest, and fresh sliced dates if desired. Serve chilled.