Prepare two large baking sheets by lining them with parchment paper. Set aside.
Place Chex cereal in a large bowl. Set aside.
Melt butter in a large saucepan over medium heat. Add corn syrup, brown sugar and salt and stir to combine.
Continue cooking over medium heat, stirring often, until it boils. Once it comes to a full boil, boil for 1 minute.
Remove from heat and add baking soda while stirring.
Pour caramel mixture over top of cereal. Stir until cereal is completely coated.
Stir in peanuts.
Spread caramel-covered cereal out between the two lined baking sheets. Sprinkle M&Ms over top.
Allow to cool.
Break into small chunks and store in an airtight container for up to 3 days.
