Pour cereal into a very large mixing bowl and set aside.
Combine brown sugar, cinnamon, butter, and corn syrup in a small saucepan. Bring to a boil, stirring constantly. Remove from heat and stir in soda and vanilla. Pour over cereal and stir lightly till all pieces are coated.
Spread onto a greased cookie sheet with sides. Mine is 15x10". Bake at 250° for about 30 minutes, stirring every 10 minutes.
Pour onto parchment paper to cool.
Melt white chips in a glass bowl in the microwave at 50% power, stirring every 30 seconds. Drizzle over cooled Chex mix.