Steps to make the caramel:
First, remove the paper from the cans of condensed milk.
Place the cans in your Instant Pot or slow cooker.
Add water to the Instant Pot or slow cooker filling it up to cover the cans.
Place the top on your device and set it for 8 hours. (If using the Instant Pot, choose the slow cook setting and set the time to eight hours.)
After 8 hours, remove the cans from the device, dry them with a towel and allow them to cool.
Once they are warm to the touch, they can be opened.
Steps to make the cake:
Preheat your oven to 350 degrees.
Using a hand or stand mixer, cream the butter, oil, and sugar together until light and fluffy (approximately 5 minutes).
Then mix in the vanilla.
Add the eggs to the bowl one at a time mixing until combined after each addition.
Add the baking powder and salt to the cake flour and whisk it together.
Add the flour mixture to the bowl alternating with the sour cream beginning and ending with flour.
Spray three 9-inch round cake pans with baking spray and pour the cake batter into the cake pans evenly.
Bake in preheated oven for 20-25 minutes or until fully baked.
The cake is done once an inserted toothpick comes out clean. Allow the cakes to cool in the pans for 10 minutes before inverting.
Then remove the cakes from the pans and allow them to continue to cool completely.
Once the cakes have cooled, layer the cake placing caramel in between each layer and place the caramel over the top and sides of the cake spreading the caramel as evenly as possible.
Serve and enjoy!