Combine brown sugar, butter, and corn syrup in medium, heavy-duty sauce pan.
6 Bring to boil over medium heat, stirring constantly.
7 Boil without stirring for 5 minutes.
8 Remove from heat.
9 Stir in vanilla extract and baking soda.
10 Pour evenly over cereal mixture; stir to coat.
11 Bake for 45 minutes, stirring every 15 minutes.
12 Cool completely in pan, stirring frequently to break apart mixture.
13 Stir in chocolate chips and pretzels.
14 Store in airtight container.