01 - Combine chopped dates and 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 chilled bowl, whip cold heavy cream using an electric mixer or whisk until soft peaks form. Place in refrigerator to maintain stability.
03 - Whisk egg yolks and granulated sugar in a separate bowl until pale and thickened, approximately 3-4 minutes. Stir in orange blossom water and lemon zest until incorporated.
04 - Transfer cooled date mixture to a food processor or blender. Process until smooth paste forms. Fold date paste into egg yolk mixture until thoroughly combined.
05 - Gently fold whipped cream into date-yolk base in two additions, using a spatula with lifting motion to maintain airiness. Continue folding until no white streaks remain.
06 - Using a clean bowl and whisk attachment, beat egg whites to stiff glossy peaks. Carefully fold whites into mousse base, preserving maximum volume for light texture.
07 - Divide mousse evenly among individual serving glasses or bowls. Smooth tops with back of spoon for even presentation.
08 - Refrigerate for minimum 2 hours or until completely set and firm to the touch. For best results, chill overnight to develop flavors.
09 - Sprinkle chopped pistachios over mousse surface. Top with freshly grated orange zest and additional sliced dates if desired. Serve chilled.