Crush the Nilla wafers and graham crackers into fine crumbs.
Combine crumbs, brown sugar, salt, and melted butter until the mixture resembles wet sand.
Press the crust mixture firmly into the bottom of a springform pan and chill in the refrigerator while preparing the filling.
In a small bowl, whisk the cornstarch with water to create a slurry.
In a saucepan over low heat, gently warm the sweetened condensed milk and stir in the cornstarch slurry until thickened, then let cool.
In a large bowl, beat the cream cheese and mascarpone until smooth.
Fold the cooled condensed milk mixture and vanilla extract into the cheese mixture until fully incorporated.
Spread a thin layer of filling over the chilled crust.
Add a layer of sliced bananas over the filling, then top with the remaining cream cheese mixture.
Smooth the top and refrigerate for at least 4 hours or overnight until set.