Preheat your oven to 250ºF (120ºC).
In a large mixing bowl, combine the Crispix cereal and pecan halves.
In a large saucepan over medium-high heat, combine brown sugar, corn syrup, and butter. Bring to a boil, stirring occasionally.
Once boiling, remove from heat and stir in vanilla extract and baking soda.
Pour the syrup over the cereal and pecan mixture and toss to coat.
Transfer the coated mixture into a 9x13 inch baking pan, spreading evenly.
Bake for 1 hour, stirring every 20 minutes.
Remove from oven, pour onto wax или parchment paper to cool.