Preheat oven to 250°F. Spray a large baking sheet (or two medium baking sheets) with non-stick cooking spray; set aside.

In a large mixing bowl, combine the Crispix and pecans; set aside.

In a medium saucepan, combine the brown sugar, corn syrup, and butter. Heat over medium heat until the mixture comes to a boil, stirring often.

Remove the sugar mixture from the heat and add the vanilla extract, then stir in the baking soda until fluffy.

Pour over the Crispix and pecans and toss to coat.

Spread the Crispix mix evenly onto the prepared baking sheets. Bake at 250°F for 1 hour, stirring every 20 minutes.

Remove the baking sheets from the oven and transfer the mix onto wax paper or parchment paper to cool to room temperature. Break larger chunks into bite-sized pieces if needed.

Store in an airtight container at room temperature for up to 1 week.