Instructions

1. For the cake: Preheat the oven to 350° F. Grease three 8-inch pans.
2. Chop the zucchini into one inch thick pieces and throw into a food processor. Pulse the zucchini into tiny pieces and set aside.
3. In a medium-sized mixing bowl, combine the vegetable oil, eggs, egg whites, vanilla extract and granulated sugar. Whisk together until well combined, and mixture turns lighter in color.
4. Add the sour cream and mix until combined.
5. Slowly add the cocoa powder and beat into the batter.
6. In a separate small bowl, combine the flour, cinnamon, salt, baking soda and baking powder and whisk together. Slowly add the dry ingredients and mix slowly with a spatula until about half of the flour is incorporated. Add the zucchini pieces and mix only until the flour is blended, being careful not to over mix.
7. Pour the batter into the three 8-inch pans, dividing evenly, and bake at 350°F for 18 to 22 minutes. To see if the cake is done, stick a toothpick into the cake and if the toothpick comes out clean, the cake is done. Cool completely.
8. For the frosting: Remove 4 sticks of butter of the refrigerator, one stick will be browned and the other 3 will be left to soften.
9. To brown the butter, use a small saucepan, and cut the butter into pieces. Melt the butter over medium heat and allow it to boil and bubble. Once it’s starts boiling, stir it frequently and it will slowly start to turn an amber color and releases a nutty aroma. Remove the butter from the heat and allow it to cool completely.
10. Cut the remaining butter into pieces. Using the paddle attachment of your stand mixer, whip the butter for 3-4 minutes, scraping down the bowl occasionally. Beat until the butter looks light in color.
11. Add 4 cups powdered sugar, one cup at a time and mix on low speed until incorporated into the butter. The frosting will be thick. Add 1 tablespoon of heavy whipping cream and continuing beating.
12. Next , add 2 cups of powdered sugar and slowly pour the cooled brown butter into the frosting and beat it into the butter until the frosting is completely smooth.
13. Add the last 1-2 cups of powdered sugar followed by 1 tablespoon of heavy cream and a pinch of salt and beat on low speed until the cream is incorporated. Then beat it at a high speed for 1 minute to whip some additional air into the frosting.
14. To build the cake: Even out the top of the cake by cutting off the dome using a serrated knife.
15. Place a dollop of frosting on the bottom of the cake plate and place the bottom layer of cake on top. The frosting will help prevent the cake from sliding.
16. In order to create even layers, I use a large piping bag fitted with an open round tip, or simply cut off the end of the piping bag. I also highly suggest to use a lazy Suzan to rotate the cake as you work.
17. Fill the first layer of frosting by using your piping bag and pipe from the outside edge into the center. Gently spread the frosting with an offset spatula to fill in the gaps.
18. Place the next layer of cake on top and repeat the above instructions to fill the second layer of frosting.
19. For the top layer of cake, place it inverted, so the bottom of the cake is actually the top, creating a nice and smooth top edge.
20. Proceed to add your crumb coat by adding a cup of frosting to the top of the cake and gently spread out to the edges and down the sides. Use the leftover frosting in your piping bags to fill in the cracks between the layers.
21. Using an offset spatula or icing smoother, wipe away the excess frosting, leaving just enough to coat the outside of the cake. Do not mix your crumb coating frosting back into your icing if it has cake debris in it. Refrigerate the cake for 15-20 minutes to allow the crumb coat to harden.
22. Remove the cake from the refrigerator and proceed to add the remaining frosting to the top and edges of the cake. To get a nice smooth edge, use your offset spatula and icing smoother to wipe away excess frosting
23. Take the chopped walnuts and press into the sides of the cake. Sprinkle the top with mini chocolate chips or additional walnuts.