Preheat your oven to 350°F (175°C). In a food processor, combine all-purpose flour, powdered sugar, unsalted butter, and salt until the mixture resembles coarse crumbs. Press this blend into the bottom of a greased 9-inch springform pan and bake for 15–18 minutes until lightly golden. Allow the crust to cool completely.

In a small bowl, bloom gelatin by mixing it with water and letting it sit. Gently warm the lemon juice on the stove until warm, then dissolve the bloomed gelatin in it. Whip heavy cream with sugar and lemon zest until stiff peaks form. Beat cream cheese until smooth, then fold in the gelatin mixture followed by the whipped cream.

In a medium saucepan over medium heat, combine fresh blueberries, sugar, and extra lemon juice. Cook for about 5–7 minutes until the blueberries soften and burst, creating a compote. Let it cool to room temperature.

Once the shortbread crust has cooled, pour the lemon mousse over it and spread evenly. Follow with a layer of blueberry compote, covering the mousse. Repeat the layers for presentation, finishing with blueberry compote. Chill the cake for at least 4 hours until set.

Run a knife around the edge of the springform pan to loosen the cake. Release the springform and slice into wedges. Serve each slice chilled, garnished with fresh blueberries or whipped cream.