Prepare the Shortbread Crust

1. In a bowl, mix shortbread crumbs, melted butter, and sugar until combined.
2. Press the mixture firmly into the bottom of a 9-inch springform pan. Chill in the fridge while preparing the mousse.

2. Make the Lemon Mousse

1. Bloom the Gelatin – Sprinkle gelatin over cold water and let sit for 5 minutes. Then microwave for 10 seconds until dissolved.
2. Whip the Cream – In a bowl, beat heavy whipping cream until stiff peaks form. Set aside.
3. Prepare the Cream Cheese Mixture – In another bowl, beat cream cheese, sugar, lemon juice, lemon zest, and vanilla until smooth.
4. Combine – Stir in the dissolved gelatin, then gently fold in the whipped cream until smooth and fluffy.
5. Assemble – Pour the mousse over the crust, spreading evenly. Refrigerate for at least 4 hours or until set.

3. Make the Blueberry Topping

1. In a saucepan, combine blueberries, sugar, and lemon juice. Cook over medium heat until berries soften and release juices (about 5 minutes).
2. Mix cornstarch with water, then stir into the blueberries. Simmer until thickened. Let cool completely.

4. Assemble & Serve

1. Once the mousse is set, spread the cooled blueberry topping evenly over the cake.
2. Chill for another 30 minutes before slicing and serving.