Preheat the oven to 350℉. Prepare four 8" cake pans with either non-stick cooking spray or butter and flour.
Using the bowl of a stand mixer, cream the butter, vegetable oil, and sugar on medium speed until soft and fluffy, about 5-6 minutes.
Next, add the flour and mix well.
Add the eggs, one at a time mixing well between each egg.
Add the baking powder, salt, sour cream, and Salted Caramel Bourbon. Mix until well blended. Do not overmix.
Pour the cake mix evenly into the four prepared cake pans. Bake for 20 minutes or until a toothpick when inserted comes out clean. Once cakes are done, remove from oven and allow to cool in the pan for 5 minutes and then on wire racks until completely cool.
Heat granulated sugar in a medium saucepan over medium heat, stirring constantly with a high heat resistant rubber spatula or wooden spoon. Sugar will form clumps and eventually melt into a thick brown, amber-colored liquid as you continue to stir. Be careful not to burn.
Once sugar is completely melted, immediately add the butter. Be careful in this step because the caramel will bubble rapidly when the butter is added.
Stir the butter into the caramel until it is completely melted, about 2 minutes. If you notice the butter separating, remove from heat and vigorously whisk to combine it again. (If you’re nervous for splatter, wear kitchen gloves.)
Very slowly drizzle in 1/2 cup of heavy cream while stirring. Since the heavy cream is colder than the caramel, the mixture will rapidly bubble when added. Allow the mixture to boil for 1 minute. It will rise in the pan as it boils.
Remove from heat and stir in 1 teaspoon of salt. Allow to slightly cool down before using. Caramel thickens as it cools.
Cover tightly and store for up to 1 month in the refrigerator. Reheat in the microwave or on the stove to desired consistency.
In the bowl of a stand mixer, combine the heavy cream, powdered sugar, and Salted Caramel Bourbon. Mix on medium speed until soft peaks form. Add the mascarpone and beat until stiff and completely smooth.
Start by placing a cake layer on a cake plate. Top with 1/4 cup of the icing and continue until all cake layers are used. Ice the cake with the remaining icing and top with the caramel sauce. Add more piped icing in a rosette and top with a truffle.
Serving Size 1 slice