Line a 9×13 pan with parchment paper and lightly mist with nonstick cooking spray. Set aside.
In a large pot, melt the butter until it begins to brown. Be careful not to let it burn.
Stir in the vanilla extract, salt, and marshmallows until completely melted.
Gradually add the Rice Krispies, stirring until everything is evenly combined.
Pour ⅓ of the mixture into the pan, sprinkle 1 cup of chopped mini candy bars, then add another ⅓ of the mixture and the remaining 1 cup of candy bars. Top with the remaining Rice Krispies.
Gently push the mixture into the pan using lightly wet hands.