Preheat oven to 350°
Spray 9x13 baking pan with cooking spray, or line with foil and spray foil to easily take bars out of pan to cut squares.
In large bowl, combine butter, one egg and cake mix. Mixture will be very stiff, so you might opt to use your hands (which I did.)
Reserve 1 cup of cake mixture for crumble topping, set aside.
Press the remaining cake mixture in the bottom of the pan and bake for 10 minutes.
While crust is baking, in a mixing bowl using mixer, beat cream cheese, sugar, vanilla, lemon juice and remaining egg until smooth.
Spread cream cheese mixture over top the partially baked crust.
Evenly arrange the blueberries over the cream cheese mixture and the sprinkle with remaining crumbles.
Bake for 25-30 minutes until center is set and crumbles on top turn golden brown.
Cool completely on wire rack.
Chill approximately 30 minutes before serving.