Let's cook.
In a small bowl, sprinkle gelatin powder over 2 tablespoons of cold water. Let it sit for 5 minutes to bloom.
In a medium saucepan, gently heat the yuzu juice and granulated sugar over low heat, stirring until the sugar dissolves completely. Do not boil.
Remove the saucepan from heat and stir in the bloomed gelatin until it is fully dissolved. Let the mixture cool to room temperature, about 15 minutes.
In a separate large bowl, whip the cold heavy cream with an electric mixer on medium-high speed until soft peaks form, about 3-4 minutes.
Gently fold the cooled yuzu-gelatin mixture into the whipped cream until just combined. Be careful not to deflate the cream.
Divide the mousse evenly into 4 small serving glasses or ramekins. Chill in the refrigerator for at least 3 hours, or until set.
Garnish with fresh yuzu zest, if desired, before serving.
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