Preheat oven to 325 and prepare three 8″ round cake pans with cooking spray and parchment paper lining the bottoms.

For the Cake:

In a stand mixer with paddle attachment, or with a hand held mixer, mix butter and sugar until light and fluffy; about 3-4 minutes.  Add the eggs one at a time, followed by the vanilla and the vegetable oil.  Blend well and then add the dry ingredients of flour, baking powder, baking soda, and salt.  Stir in the buttermilk and the white chocolate liqueur.  Divide batter evenly between the three pans and bake for approximately 25 minutes.  You want the cake to rise and be done in the middle, but not appear too dark.  An overbaked cake is a dry cake.  Let the layers sit and cool for 5-10 minutes before turning them out of the pans.  Once removed from the pans, brush with simple syrup.

For the Simple Syrup:  In a small sauce pan, bring the sugar and water to a boil just until you can see the sugar has dissolved.  Remove from heat and add the white chocolate liqueur.

For the Filling:

In a bowl or a saucepan, warm the heavy cream to steaming, but not boiling.  This is one of the few things I actually use my microwave for.  Add the chocolate chips and let sit for 1-2 minutes to melt.  Stir the melted chocolate and cream together and add the peppermint oil.  Set aside to cool.  This will need to be at room temperature or cooler to use as filling.  You can speed up the process by placing the bowl in the refrigerator, remembering to stir the mixture occasionally.

For the Buttercream:

In a stand mixer or with a handheld mixer, mix the butter, powdered sugar, vanilla and salt.  Mix it until it is light and fluffy.

To Assemble:

Make sure all cake layers and filling are cooled to room temperature.  Place one layer of the cake on a plate or stand and pipe buttercream around the edge to act as a dam for the filling.  Place half of the ganache on the cake layer and top with cake layer #2.  Repeat with the buttercream and filling, finishing with a cake layer for the top.  Use more buttercream to frost the top and sides of the cake.  I encourage creating a crumb coat and letting that chill for 10 minutes before continuing with more frosting and decoration.  After frosting your cake, you could add the optional chocolate drip. Melt the chocolate chips in warm heavy cream.  Spoon the warm chocolate onto the cake, or use a bottle/dispenser to create drips.  Use decorative tips to pipe frosting rosettes on top, wedge pieces of peppermint bark onto the top of the cake, and crush candy canes to sprinkle on the sides and top.  Have fun and be creative!