Make the crust
Mix the graham cracker crumbs, melted butter, and sugar in a bowl until the texture resembles wet sand.
Press the mixture into the bottom of a 9-inch springform pan using a flat-bottomed glass.
Refrigerate while preparing the filling.
Prepare the blueberry layer
Combine blueberries, sugar, lemon juice, and water in a saucepan over medium heat.
Bring to a simmer, then stir in the cornstarch. Let it gently bubble until thickened like jam.
Remove from heat and let it cool completely.
Make the lemon cream filling
Beat the softened cream cheese until smooth.
Add sweetened condensed milk, lemon juice, lemon zest, and vanilla. Mix until creamy.
In a separate bowl, whip the heavy cream until stiff peaks form.
Gently fold the whipped cream into the lemon mixture until fully combined.
Assemble the cake
Pour half the lemon cream mixture over the chilled crust and smooth it.
Dollop half the blueberry sauce on top and gently swirl with a butter knife.
Add the remaining lemon cream, smooth the top, and swirl in the rest of the blueberry sauce.
Chill and serve
Cover the cake and refrigerate for at least 6 hours or overnight.
When ready to serve, run a knife around the pan and release the springform.
Garnish with whipped cream, blueberries, and lemon zest if desired.