Heat oven to 350°F. Line 8-inch square pan with foil, extending foil over 2 opposite sides of pan. Spray foil with cooking spray.
Place block of cookie dough in bottom of pan. Gently press dough with fingers to flatten and cover bottom of pan in even layer.
Bake 18 minutes or just until center is set.
Sprinkle marshmallows over partially baked crust. Arrange pretzels over marshmallows in 5 or 6 rows of 5 pretzels each. Sprinkle chocolate chips over top.
Return to oven; bake 5 minutes longer. For a toasted marshmallow appearance, set oven control to broil. Place pan on top oven rack; broil 1 to 2 minutes or until marshmallows are light golden brown, watching constantly to prevent burning. (Even 30 seconds can make or break it and cause marshmallows to burn.)
Cool bars in pan at least 30 minutes.
Lift bars from pan by using foil overhang; place on cutting board. Cut either into 3 rows by 3 rows to make 9 bars or into 4 rows by 3 rows to make 12 bars. Store in airtight container at room temperature up to 5 days.