Preheat oven to 350 degrees. Grease the bottom and sides of a 9 x 11 metal baking pan. Cut parchment paper to size, leaving a couple inches overlapping each end. Grease the parchment paper, too.
In a heavy-bottom sauce pan, melt the butter and 12 ounces of the dark chocolate over low heat. Stir very frequently until the mixture is smooth and completely melted. Remove from heat and let cool.
In a large mixing bowl, beat together eggs, sugar, and vanilla until creamy, about 2 minutes.
Slowly pour the melted chocolate mixture into the egg mixture. Beat 2 - 3 minutes until well combined.
Add the flour to the brownie mixture, and stir until combined. Fold in the dark chocolate chips and ½ CUP of the white baking chips.
Evenly spread the brownie batter into the prepared baking pan. Sprinkle the top generously with the remaining white baking chips.
Place in the oven and bake for 5 minutes. Remove from the oven and swirl the melted white chips into the brownie batter.
Return the brownies to the oven and bake for 25 - 30 minutes. (I cooked ours for 28 minutes. The time will vary based on your oven. Don't go over 30 minutes. Remember, the brownies will continue to cook in the pan after you remove them from the oven.) Allow the brownies to cool for 20 minutes (if you can stand it) in the pan.
For the Salted Caramel Drizzle
While the brownies are cooling, in a small non-stick skillet, heat water and sugar over medium heat. Do not stir the sugar water, but gently swirl it every few minutes. Cook for 15 minutes or until a deep, golden brown.
Remove the skillet from heat and gradually stir in the heavy cream. Add a pinch of sea salt, stir.
Lift the brownies from the pan by carefully grasping each end of the parchment paper. Transfer to a flat surface.Drizzle the top with the salted caramel and cut into squares.