Whip butter, sugar, vanilla and orange zest together until creamy
Mix together until mixture is combined and batter resembles cookie dough
Add eggs, caramel sauce, and sour cream
Whisk together until smooth
Pour into well greased and floured bundt cake pan
Bake at Fahrenheit 325° 45-60 minutes until cake is lightly browned and springs back at the touch
Let rest in pan for 10 minutes
Invert on a wire rack
Pour ¼ cup of caramel sauce over hot cake
Let rest until cooled
Caramel Sauce (Optional)
Melt all ingredients in a large saucepan, minus ½ of heavy whipping cream, on medium heat
Bring to a boil and cook for 5 minutes, stirring constantly
When mixture is starting to become difficult to stir, add in remaining ½ cup of cream
Cook 5-7 minutes more until soft ball stage, or until the mixture drips slowly off of your wooden spoon
Notes
Soft ball stage is when a teaspoon of caramel is dropped into cold water. The caramel will immediately set. If it separates it needs to continue cooking. If it is soft and malleable it is ready to go. If it cracks it's overdone.