01 - Combine chopped dates and water in a small saucepan. Cook over low heat for 3-4 minutes, stirring constantly until dates break down into a soft, jammy consistency. Remove from heat and allow to cool completely to room temperature.
02 - In a chilled large bowl, whip cold heavy cream using an electric mixer or whisk until soft peaks form. Refrigerate immediately to maintain structure until needed.
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 lemon zest, whisking until fully combined.
04 - Process the cooled date mixture in a food processor or blender until completely smooth, scraping down sides as needed. Fold the pureed dates into the egg yolk mixture until thoroughly incorporated.
05 - Gently fold the chilled whipped cream into the date-yolk base in two separate additions, using a spatula with a light lifting motion to maintain airiness and prevent deflation.
06 - In a pristine grease-free bowl, whisk egg whites until stiff glossy peaks form. Delicately fold the whipped whites into the mousse base using minimal strokes to preserve maximum volume.
07 - Divide the mousse evenly among individual serving glasses or dessert bowls, using a spoon to smooth the tops.
08 - Refrigerate mousse for minimum 2 hours or until completely set and firm to the touch. For best results, chill overnight to allow flavors to meld.
09 - Just before serving, sprinkle chopped pistachios and finely grated orange zest over each portion. Arrange additional sliced dates on top as desired.