The Shortbread Crust:

• Preheat your oven to 350°F (175°C). Grease and line a 9-inch springform pan with parchment paper.
• Combine the all-purpose flour, powdered sugar, unsalted butter, and a pinch of salt in a food processor. Pulse until the mixture resembles coarse crumbs.
• Press the mixture evenly into the bottom of the prepared pan and bake for 15-18 minutes, or until lightly golden. Allow it to cool completely.

The Lemon Mousse:

• Sprinkle gelatin powder over the water in a small bowl and let it bloom for 5 minutes.
• Heat lemon juice over low heat in a saucepan until warm, then stir in the bloomed gelatin until dissolved. Allow this mixture to cool to room temperature.
• In a mixing bowl, beat heavy cream, granulated sugar, and lemon zest until stiff peaks form.
• In another bowl, whip the cream cheese until smooth. Gradually add the lemon juice mixture, continuing to beat until smooth. Finally, fold in the whipped cream until fully incorporated.

For the Blueberry Compote:

• Combine blueberries, sugar, and lemon juice in a saucepan. Cook over medium heat, stirring occasionally, until the blueberries soften and release their juices (about 5-7 minutes). Allow it to cool to room temperature.

Assembling the Mousse Cake:

• With the crust cooled, begin by spreading a layer of lemon mousse, then a layer of blueberry compote. Continue layering, finishing with compote on top.
• Refrigerate the cake for at least 4 hours, or until set.
• Before serving, run a knife around the edge of the pan to loosen the cake. Carefully remove the sides, slice, and serve chilled.