Zucchini Chocolate Cake 

Preparation

1. Make the cake:

   1. Step 1

      Heat the oven to 350 degrees. Grease three (8-inch) round cake pans and line the bottoms with parchment paper.

   2. Step 2

      In a medium bowl, whisk together the flour, cocoa, baking soda and salt. Set aside.

   3. Step 3

      To the bowl of a stand mixer fitted with the paddle attachment (you could also do this in a large bowl with an electric hand mixer), add the butter, granulated sugar, brown sugar and vanilla; beat on medium speed until light and fluffy, about 2 minutes. Add the olive oil and eggs and mix until combined, about 15 seconds. Beat in the buttermilk and flour mixture in two additions each, alternating between them, and then continue to mix until the batter is completely combined. Fold in the grated zucchini.

   4. Step 4

      Divide the batter amongst the three cake pans (about 2¼ cups/546 grams batter per pan; no need to weigh, but it does ensure you have perfectly even layers).

   5. Step 5

      Transfer the cake pans to the oven to bake until a skewer or cake tester inserted into the center comes out clean, 27 to 30 minutes. Let cool for 5 minutes before inverting them onto cooling racks. Let cool completely for at least 1 hour before frosting the cake. Remove the sheets of parchment just before assembling.

2. Make the frosting: 

   1. Step 6

      Add the butter to the bowl of a stand mixer (or a medium bowl with an electric hand mixer) and beat on medium speed until smooth, about 30 seconds. Remove the paddle attachment and place a fine-mesh sieve on top of the bowl and sift in the powdered sugar. Turn the mixer to low and beat until the powdered sugar is almost completely incorporated. Add the vanilla bean seeds and heavy cream; and beat once more until combined, about 1 minute.

3. Assemble the Layer Cake: 

   1. Step 7

      If any of the cooled cakes have domed tops, feel free to level them with a serrated knife to make three even, flat layers. To assemble, place one cake layer on a serving plate or cake stand (see Tip) and use an offset spatula to spread the top evenly with about ⅔ cup of the frosting. Repeat with the second cake layer and another ⅔ cup of frosting, then top with the third cake layer.

   2. Step 8

      Apply a “crumb coat” to the cake: Use ½ cup frosting to apply a thin, even coat of frosting to the outside of the cake, then transfer to the fridge to chill for 20 minutes (this will firm up the frosting). Spread the remaining buttercream (about rounded 2 cups) over the cake (To add piped decorations, see Tip.)

   3. Step 9

      You can serve it right away, but for the cleanest cuts, refrigerate the cake for at least an hour (or up to 4 hours). If storing for longer, lightly cover the outside with plastic wrap to prevent the buttercream from drying out. Bring the cake to room temperature again before serving.