01 - Sprinkle powdered gelatin over cold water in a small bowl and allow to bloom for 5 minutes.
02 - Heat pumpkin purée, whole milk, granulated sugar, ground cinnamon, ground nutmeg, ground ginger, ground cloves, vanilla extract, and salt in a medium saucepan over medium heat. Stir until sugar fully dissolves and mixture is warm; do not boil.
03 - Remove the saucepan from heat. Stir in the bloomed gelatin until fully dissolved. Cool mixture to room temperature.
04 - In a clean bowl, beat egg whites with an electric mixer until stiff peaks form.
05 - Whip heavy cream in a separate bowl until soft peaks form.
06 - Gently fold whipped cream into the cooled pumpkin mixture. Then, carefully fold in the beaten egg whites until the mousse is light and smooth.
07 - Spoon or pipe the mixture into serving cups. Cover and refrigerate for at least 2 hours, until set.
08 - Before serving, top each mousse cup with whipped cream, crushed ginger snap cookies or toasted pecans, and a sprinkle of ground cinnamon, as desired.