01 - Combine chopped dates and water in a small saucepan. Cook over low heat for 3-4 minutes, stirring frequently until dates soften into a jam-like 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 and granulated sugar in a separate bowl until mixture becomes pale yellow and thickened, approximately 3-4 minutes. Incorporate orange blossom water and lemon zest, whisking until fully blended.
04 - Transfer cooled date mixture to a food processor or blender. Process until completely smooth, scraping down sides as needed. Fold the date paste into the egg yolk mixture until homogeneous.
05 - Gently fold one-third of the refrigerated whipped cream into the date-yolk base to lighten the mixture. Fold in remaining whipped cream in two additions, using a spatula with gentle sweeping motions to maintain airiness.
06 - In a pristine, grease-free bowl, whisk egg whites until stiff, glossy peaks form. Carefully fold the whipped egg whites into the mousse base using minimal strokes to preserve 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, sprinkle chopped pistachios and finely grated orange zest over the surface. Add sliced dates as additional garnish if desired.