Spray a 9X13 baking pan with a non-stick cooking spray.
Place the popcorn in a large mixing bowl and remove any unpeopled kernels.
Stir in the peanuts and M&Ms. Set aside.
Place the marshmallows and butter in a separate microwave safe bowl. Heat in 30 second intervals, stirring after each interval until the mixture is fully melted and combined.
Then stir in the vanilla extract and salt.
Pour the marshmallow mixture over the popcorn mixture and gently stir to coat.
Press the mixture into the bottom of the pan.
Let the mixture sit at room temperature for 1-2 hours until set.
Then the bars are ready to cut, serve and enjoy!
Notes
Store in an airtight container at room temperature for up to 3-4 days.