STEP 2:
Beat butter & sugar, then add oil and continue beating. Add eggs, one at a time while beating, then add sour cream & vanilla extract & beat until combined.
STEP 3:
Add half of the dry ingredients to the wet ingredients, mix on low speed, then pour in milk, followed by the rest of the dry ingredients. Fold in the chocolate chips.
STEP 7:
Pipe a border of buttercream on the 1st layer. Spread a layer of bourbon caramel sauce in the border, then top with buttercream. Repeat with 2nd layer.