Marble Olive Oil Cake

1. Preheat the oven to 325F(165C). Grease and line three 6-inch round cake pans with circle parchment paper cutouts.
2. In a large mixing bowl, whisk to combine the flour, baking powder, baking soda, and salt. In a separate medium mixing bowl, whisk the cocoa powder and hot water until smooth. Set aside to cool.
3. Using a stand or hand mixer, mix the sugar and oil together at medium speed to combine, about 1 minute. Next, mix in the vanilla extract followed by the eggs one at a time stopping to scrape the bottom and sides of the bowl with a silicone spatula after each addition.
4. Reduce the mixer speed to low. Starting and ending with the dry ingredients, mix half of the dry ingredients into the wet batter followed by all of the buttermilk and ending with the remaining dry ingredients.
5. Stop the mixer and scrape the bottom and sides of the bowl with a silicone spatula. Increase mixer speed to medium and mix the batter for an additional 1-2 minutes to ensure that you have a smooth, lump-free mixture.
6. Scoop 1 1/2 cups of the vanilla cake batter into the bowl with the cooled chocolate mixture and gently mix until thoroughly incorporated. Divide the batters equally between the 3 prepared pans,alternating between the vanilla and chocolate cake batter.
7. Using the tip of a sharp knife or skewer, swirl the chocolate and vanilla cake batters together (see photos above for reference). Bake the cake batter for 30 to 35 minutes, or until a toothpick inserted in the center of a cake comes out clean or with a few moist crumbs.
8. Cool the cakes in the pans for 15-20 minutes before transferring to a cooling rack to cool to room temperature.

Chocolate Buttercream Frosting

1. Using a stand or hand mixer, cream the butter and salt at medium high speed until it is smooth and fluffy in appearance, about 2-3 minutes.
2. Reduce the mixer speed to low and mix in the confectioners’ sugar and cocoa powder into creamed butter. Gradually increase the mixer speed back to medium.
3. Once all the sugar and cocoa powder have been incorporated into the butter, mix in 5 tablespoons of the heavy whipping cream and vanilla extract into the buttercream.
4. If buttercream appears too thick, mix in additional cream 1/2 tablespoon at a time until the desired consistency (thick but spreadable) is reached. If buttercream appears to be too soft, mix in additional confectioners’ sugar 1/4 cup at a time until a thick but spreadable consistency is reached.
5. Increase mixer speed to medium high and mix chocolate buttercream for an additional 30-60 seconds. The resulting buttercream should be smooth and fluffy in appearance.

Assembly

1. Level cooled cakes with a serrated knife or cake leveler. Spoon about 1/2 cup of the buttercream into the center of the first cake layer and smooth out into an even layer. Place the second cake layer face up on top of the buttercream and repeat the process one more time.
2. Place the final cake layer top side down over the buttercream. Apply a thin layer of buttercream over the entire surface of the cake for a crumb coat and refrigerate to set for 30-60 minutes.
3. Apply a thick layer of the remaining buttercream over the entire surface of the chilled cake and smooth out using a bench scraper and offset spatula.
4. Place the cake in the fridge and make the chocolate ganache (see this post for method). Allow the chocolate ganache to thicken for 5-6 minutes before dripping around the border of the cake. Pipe remaining buttercream in desired pattern on top of the cake and fill the center with as much of the remaining ganache as you can.
5. Lightly top piped border with chocolate sprinkles (optional) before serving.