Preheat oven to 300 degrees. In a large bowl, mix together cake mix, 1 egg, butter, vanilla extract, and half a can of caramel sweetened condensed milk. Mix will be thick but spreadable. Spread in the bottom of a greased 9x13" glass dish.
In another bowl, mix caramel bits and the rest of the can of sweetened condensed milk. Melt in the microwave in 30-second increments until smooth. Pour over the cake mixture in the glass dish and spread; sprinkle the sea salt over the top. Allow to set for 10-15 minutes.