In a large mixing bowl, cream butter, oil and sugar on high until fully incorporated and light and fluffy, about 5-6 minutes.
Turn mixer to medium speed and mix in eggs one at a time until well incorporated.
Add in vanilla extract and mix.
Sift cake flour, baking powder and salt into a medium sized bowl.
With mixer on slow speed, alternate adding in flour mixture and sour cream ending with flour mixture until mixed through.
Do not over mix.
Spray Bundt cake pan with baking spray or grease and flour them.
Pour batter into cake pans and spread evenly.
Bake in preheated oven for 1 hour and 30 minutes or until fully baked (but DON'T OVER-BAKE THIS DELICIOUS CAKE- CHECK THEM EARILER SO THEY DON'T DRY OUT). TAKE A TOOTH PICK AND STICK IT INSIDE THE CAKE AFTER ONE HOUR TO DEE IF IT COMES OUT CLEAN.
Remove cake pans from oven and cool on cooling racks for 10 minutes.
Remove cakes from pans and wait until completely cooled to ice.
For the Caramel Icing:
Add butter, evaporated milk, and sugar to saucepan over medium heat until everything has melted together.
Leave over medium to low heat stirring periodically for about 1 1/2- 2 hours (watch the entire time to make sure it does not burn or stick but ... cook until thickened and caramel has darkened to a lovely golden brown.
Make sure that the caramel turns Nice and golden like the color of this cake in this photo before stopping the heat.
It should also thickly coat the back of a spoon to ensure thickness.
Be careful to watch, adjusting heat temperature to not let it burn.
Remove from heat and add in vanilla extract.
Cool for about 15-20 minutes to allow it to thicken before icing the cake.