Step 1

Preheat oven to 350 degrees F Lightly grease a 13x9 inch pan.

Step 2

Make cake mix according to package directions, adding in an extra egg and ½ cup sour cream to the ingredients.

Step 3

Pour 1/2 of the cake batter into the prepared pan and bake at 350 degrees for 20 minutes.

Step 4

While cake is baking, in a heavy saucepan over low to medium heat melt caramels, heavy cream and butter. Stir well until melted and combined.

Step 5

Remove cake from oven after 20 minutes of baking and pour caramel sauce over top of baked cake. Sprinkle 1 cup chocolate chips over caramel. Pour remaining cake batter over top and return to oven to continue baking for 20 to 25 minutes more.

Step 6

Remove from oven and allow to cool for approximately five minutes.

Step 7

Combine remaining chocolate chips and sweetened condensed milk in a microwave safe bowl and microwave for one minute. Remove and stir until well combined. If chocolate chips are not completely melted return to microwave for 15 seconds, remove and stir. Repeat until melted and smooth. Stir in vanilla. Pour over the top of the cake. Allow to sit for approximately five minutes.