01 - Combine chopped dates and water in a small saucepan. Cook over low heat for 3-4 minutes, stirring constantly until dates soften into a jammy consistency. Remove from heat and allow to cool completely to room temperature.
02 - In a large chilled bowl, whip cold heavy cream using an electric mixer or whisk until soft peaks form. Refrigerate immediately to maintain structure.
03 - Whisk egg yolks with granulated sugar in a separate bowl until mixture becomes pale and thickened, approximately 3-4 minutes. Incorporate orange blossom water and lemon zest until fully blended.
04 - Process cooled date mixture in a food processor or blender until completely smooth, forming a uniform paste. Fold the date paste thoroughly into the egg yolk mixture until no streaks remain.
05 - Gently fold one-third of the chilled whipped cream into the date-yolk base to lighten the mixture. Add remaining whipped cream in two additions, folding with a spatula using gentle lifting motions to preserve airiness.
06 - In a clean grease-free bowl, whisk egg whites to stiff, glossy peaks. Carefully fold the whipped egg whites into the mousse base using a gentle folding technique, maintaining maximum volume and aeration.
07 - Divide the finished mousse evenly among individual serving glasses or decorative bowls, filling each vessel three-quarters full.
08 - Refrigerate mousse for a minimum of 2 hours until fully set and firm to the touch. For optimal texture, do not exceed 4 hours chilling time.
09 - Just before serving, sprinkle each portion with chopped pistachios and finely grated orange zest. Arrange additional sliced dates on top as desired for presentation.