Place the Crispix in a large microwave safe mixing bowl or large paper bag. Line two large baking sheets with parchment paper or a silpat mat and set aside.

Combine the butter, brown sugar, corn syrup and vanilla in a large saucepan. Bring to a boil over medium-high heat and allow to boil for 1 1/2 - 2 minutes, stirring frequently. Be careful not to boil too long or caramel will be too crunchy. Remove mixture from the stove and add the baking soda. The mixture will foam a bit then settle.

Add the caramel mixture to the prepared Crispix and stir gently with a rubber or wooden spatula. Place the bowl of caramel Crispix in the microwave and heat on high for 1 minutes. Remove from microwave and stir gently. Repeat 3 more times to reach a total of 4 minutes. Spread mixture evenly onto prepared baking sheets and sprinkle generously with sea salt. Allow to cool completely, breaking pieces or chunks apart with your hands or spatula as it cools. Store in an air tight container for up to 5 days.