In a bowl, combine crushed shortbread cookies with melted butter. Press into the bottom of a springform pan to form a crust. Refrigerate for 15 minutes.
Spread blueberry preserves evenly over the crust and return to the fridge.
In a large mixing bowl, beat the cream cheese, lemon zest, lemon juice, powdered sugar, and vanilla until smooth.
In a separate bowl, whip the heavy cream to stiff peaks, then gently fold into the cream cheese mixture.
Spread the mousse mixture over the blueberry layer, smoothing the top.
Chill the cake for at least 4 hours or overnight for best results.
Before serving, top with fresh blueberries and optional whipped cream.