Preheat oven to 350°F. Line 8x8-inch pan with parchment paper and spray with cooking spray.
Combine flour, cornstarch, baking soda, and salt in medium bowl. Whisk together and then set aside.
In large bowl, beat butter and sugars together. Add eggs and vanilla. Beat to combine.
Add flour mixture to butter mixture and combine.
Fold in all chocolate chips, pretzels, and caramel bits. Reserve small amount of each ingredient for sprinkling on top of cookie bars, if desired.
Spread batter into prepared pan. Top with reserved chocolate chips, caramel, and pretzel pieces.
Bake 30-35 minutes until center of cookie bars is set.
Remove from oven and allow to cool to room temperature before slicing.