• Preheat the oven to 350 degrees, grease and flour three 8×2 inch round pans.
• In a medium bowl, whisk the flour, baking powder, baking soda and salt for 30 seconds. Set aside
• In another bowl, add the buttermilk, oil and vanilla.  Set aside..
• In the bowl of your mixer, add the butter and mix at medium speed until smooth. Gradually add the sugar and continue to mix on medium speed for 3 to 5 minutes until lightened in color and fluffy. Add the eggs one at a time mixing until the yellow of the yolk disappears.
• Alternately add the flour mixture and buttermilk mixture, beginning and ending with the dry ingredients (3 additions of dry ingredients and 2 of liquid).
• Do not mix above medium speed or over mix the cake batter.
• Bake at 350 degrees for 25-30 minutes or until a toothpick inserted in the center comes out clean or with just few crumbs attached. Let cool 10 minutes and turn out.
• For the Caramel Sauce
• Using a medium size saucepan (deep enough to prevent boil over) melt the butter over medium heat.
• When the butter has melted, add the brown sugar, milk, salt, vanilla and light corn syrup
• Stir slowly trying to keep the mixture off the sides of the pan. 
• Once the mixture begins to  boil, turn the heat to low and put a lid on the pot. Simmer 5 to 6 minutes. 
• Check the pot now and then to make sure it will not boil over.  A lid on the pot steams sugar crystals from sides of the pot.
• When the time is up, remove from the heat and pour into a heat proof bowl.  It will look too thin but keep in mind that the caramel thickens as it cools. Allow to cool before using in the frosting. You can refrigerate to speed up the process. Makes about 2 cups sauce.
• Reserve ½ cup caramel for spreading onto layers when assembling the cake

For the Caramel Buttercream

• Add stick of softened butter to mixing bowl and mix until smooth. Mixing on low speed, add about half of the powdered sugar and mix until incorporated.
• Gradually add the 1 ½ cup caramel sauce and remaining powdered sugar.
• Increase to medium speed and mix for 3-4 minutes until frosting is well mixed, and has a light, creamy consistency. To reduce air bubbles, you can mix for an additional 1-2 minutes on the lowest setting as a final step.

Assemble the Cake

• Place the first vanilla cake layer on the cake plate or pedestal.
• I piped a dam of caramel buttercream around the edge of the cake layer using a disposable piping bag with the tip snipped away.
• Spread about ¼ cup of caramel within the dam on top of the cake layer (adjust amount to your liking).
• Spread caramel frosting over the caramel glazed layer. I often pipe the buttercream onto the filling and spread it but if you'd rather, you can spread the next cake layer with frosting and apply it to the first cake layer frosting-side-down. Repeat for the other cake layers.
• Fill any gaps between the cake layers with frosting (I used the same piping bag that I used for the dam for this step.)
• Apply a thin layer/crumb coat to the cake. At this point, I like to chill the cake for 10-15 minutes or refrigerate for longer.
• The chilling step firms everything up for the final coat of frosting so that you don't have to worry about the layers shifting as you decorate.
• Add the final coat of frosting- I used a small offset spatula to create swirls in the buttercream. I finished things off with a buttercream shell border (using a medium sized star tip 21).