Preheat the oven to 325 F and line a large baking sheet with either parchment paper or a Silpat sheet.
In a medium bowl sift together flour, salt, baking soda, and cornstarch. Whisk to combine, then set aside.
In a large bowl add the room temperature butter, sugar, and brown sugar. Using a hand mixer, beat until fluffy and combined.
Add eggs, yolk, and vanilla extract. Beat to combine.
Add in the flour mixture ⅓ at a time, and mix cookie dough to combine.
Finally add mini pretzels, m&ms, Chex cereal, and caramel corn. Using your hands to mix these in will work best.
Separate the cookie dough into 6 large balls.
Place on a parchment-lined baking sheet, or a Silpat.
Bake chex cookies only 3 at a time for 20 minutes.
Notes
Make sure ingredients are at room temperature and set out at least 30 minutes before starting your recipe.Bake only one cookie sheet at a time. This will result in an even cook.Experiment with different inclusions. Let me know in the comments what you mixed into your cookie dough and if you enjoyed the experience.