1. Preheat your oven to 250°F and line baking sheets with aluminum foil or silicone baking mats for easy cleanup.
2. Combine the Chex cereal, assorted nuts, and pretzels in a large mixing bowl and stir gently to mix evenly without breaking the cereal.
3. Melt the butter in a large saucepan over medium heat. Add the brown sugar, light corn syrup, and optional salt, stirring continuously until the mixture begins to boil. Let it boil for 2 minutes without stirring.
4. Remove the saucepan from heat and stir in the vanilla extract and baking soda quickly. The mixture will foam and become light and airy.
5. Pour the hot toffee mixture over the dry ingredients in the mixing bowl. Using a rubber spatula, gently fold and mix the ingredients to coat them thoroughly and evenly.
6. Spread the coated mixture evenly onto the prepared baking sheets, ensuring the layer isn’t too thick.
7. Bake the mix in the preheated oven for 30-55 minutes, stirring every 15 minutes to avoid clumping and ensure even texture.
8. Remove the mixture from the oven and allow it to cool completely on the baking sheets. Break apart any clumps for a snackable consistency.
9. Transfer the cooled mix into airtight containers or resealable bags. Store at room temperature for up to 3 days, refrigerate for longer shelf life, or freeze for up to 2 months.