01 - Preheat the oven to 350°F. Line a 9x9-inch baking pan with parchment paper, allowing excess to extend beyond the edges for easy removal.
02 - Combine vanilla wafer cookie crumbs, melted butter, sugar, and salt in a bowl until evenly combined. Press the mixture firmly into the bottom of the prepared pan.
03 - Bake the crust for 8 minutes. Remove from the oven and let cool slightly.
04 - Using an electric mixer, beat cream cheese in a large bowl until smooth. Add granulated sugar and beat until incorporated. Mix in eggs one at a time, then blend in vanilla extract and sour cream until the mixture is creamy and uniform.
05 - Pour the cheesecake mixture over the cooled crust and spread evenly with a spatula.
06 - Dollop cherry pie filling over the cheesecake layer. Use a knife or skewer to gently swirl portions of the filling and cherries into the cheesecake mixture.
07 - In a separate bowl, blend flour, granulated sugar, softened butter, milk, vanilla extract, and salt until a crumbly dough forms. Fold in rainbow sprinkles.
08 - Crumble the birthday cake dough evenly over the cherry layer.
09 - Return the pan to the oven and bake for 25 to 27 minutes, until the topping is golden and the cheesecake layer is just set.
10 - Allow bars to cool to room temperature, then refrigerate for at least 3 hours or preferably overnight before slicing into individual portions.