1. Prepare 9 inch cake pan with a parchment paper circle in the bottom and grease the sides. If you have a leakproof 9 inch springform pan, that would be best.

2. Add all dry ingredients to a large bowl and whisk together.

3. Add egg, buttermilk and vegetable oil to the dry ingredients and mix well.

4. Add vanilla to boiling water and add to mixture. Mix well.

5. Pour into cake pan and bake at 300 degrees for about 33-35 minutes, or until a toothpick comes out with a few crumbs.

6. Remove cake from oven and allow to cool for about 10 minutes, then remove to cooling rack to cool completely.

7. To make the truffle layer, put peanut butter chips into a mixing bowl.

8. Microwave heavy cream until boiling, then pour over peanut butter chips.

9. Cover bowl with clear wrap and allow to sit for 5-7 minutes.

10. Whisk mixture until smooth, then cover and place in refrigerator for about 45 minutes to an hour. It should thicken, but still be stirable.

11. Stir in mascarpone cheese until smooth.

12. Once cake has cooled, use a serrated knife to cut off the cake dome.

13. Place cake into 9 inch springform pan, lining sides of pan with parchment paper so that it sticks up above the edge of the pan.

14. Pour peanut butter mixture over cake and spread evenly. It may come above the edge of the cake pan, but your parchment paper should be high enough. Refrigerate until firm, 3-4 hours.

15. Once truffle layer is firm, remove cake from pan.

16. To make the icing, beat butter and shortening until smooth.

17. Add powdered sugar, cocoa and 1 tsp of water and mix until smooth.

18. Add more water as needed until the icing is a smooth consistency.

19. Pipe icing around the edges of the cake, then drizzle with chocolate sauce.

20. Refrigerate until ready to serve. You can let it sit out for about 15-20 minutes for the truffle layer to soften, if you prefer.