Melt the butter in a heavy-bottomed pot. Add applesauce brown sugar,corn syrup and salt. Bring to a boil, stirring constantly. Boil without stirring for 5 minutes on medium heat. Remove from heat and stir in vanilla, then add the baking soda.
Toss caramel mixture with cereal. Microwave uncovered on high 4 to 5 minutes, stirring and scraping bowl after every minute, just until cereal begins to brown.
Spread cereal out on wax paper.
Melt white chocolate in microwave safe container for 30 second increments until smooth.
Immediately drizzle over caramel chex.