Step 1

Preheat the oven to 325F (163C) and grease and line four 6 inch (15cm) round pans with baking spray and parchment paper.*

Step 2

In a large bowl, whisk together the flour, sugar, cocoa powders, baking powder and salt until they're well combined.

Step 3

In a separate large bowl, whisk together the oil, eggs, coffee and milk, until they're well combined.

Step 4

Sift the dry ingredients over the wet ingredients and then whisk together until the batter is completely smooth.

Step 5

Distribute the batter evenly among the four pans, about 12oz, in each, and bake for 35 minutes. The edges should release from the pans and the top should spring back when you press on it gently.

Step 6

Flip the cake over onto a tea towel and allow it to cool to room temperature.

Step 7

When the cakes are almost done baking, make the white cake.

Step 8

In a medium bowl, whisk together the flour, baking powder and salt until they're evenly distributed.

Step 9

Whisk together the oil and the granulated sugar in a large bowl until they're smooth.

Step 10

Add the egg whites and whisk aggressively for 1-2 minutes (or use an electric mixer), until the color lightens a little.

Step 11

Add the sour cream and vanilla extract and whisk just until combined.

Step 12

Add half of the dry ingredients to the wet ingredients, turn the mixer on low speed and then pour in the heavy whipping cream, followed by the rest of the dry ingredients. Mix just until the last streak of flour is combined.

Step 13

Prepare one more pan and pour the batter into one 6 inch round pan and bake for 35 minutes.* When the cake is fully baked it will release itself from the edge of the pan and it will spring back if you press on the center of it.

Step 14

Flip the cake over onto a wire rack or tea towel and allow the cakes to cool completely before frosting.

Step 15

Place the white chocolate into a large bowl and the dark chocolate into a separate large bowl.

Step 16

Place the heavy whipping cream into a small saucepane and heat over medium heat until it comes to a heavy simmer (bubbling all around the edge).

Step 17

Pour 2 cups over the dark chocolate and 1 cup over the white chocolate. Cover the bowls with a lid or plastic wrap for about 5 minutes, so the chocolate melts.

Step 18

Use a rubber spatula to gently stir the ganaches until they're completely smooth.

Step 19

Cover again and allow them to cool completely to room temperature.**

Step 20

Once they've cooled, use an electric mixer with the whisk attachment, at high speed, to beat the ganaches (separately) until they're fluffy and have lightened in color.

Step 21

Place the first layer of chocolate cake onto a flat surface. Spread a thin layer of the whipped white chocolate ganache on top (this is easiest with a piping bag).

Step 22

Place a layer of white cake next, topped with a layer of dark chocolate ganache.

Step 23

Next place a layer of chocolate cake, then white chocolate ganache and then another chocolate cake.

Step 24

Now spread a layer of the chocolate ganache and the second white cake.

Step 25

Last, spread a layer white chocolate ganache followed by the last chocolate cake.

Step 26

Chocolate Cake

Step 27

White Chocolate Ganache

Step 28

White Cake

Step 29

Dark Chocolate Ganache

Step 30

Chocolate Cake

Step 31

White Chocolate Ganache

Step 32

Chocolate Cake

Step 33

Dark Chocolate Ganache

Step 34

White Cake

Step 35

White Chocolate Ganache

Step 36

Chocolate Cake

Step 37

You should have a little white chocolate ganache leftover and more dark chocolate ganache. Use them to frost the outside. You can either combine them or marble them.

Step 38

Or you could do the white chocolate ganache as a crumb coat and then cover it with the dark chocolate ganache.

Step 39

If the ganache starts setting and is difficult to spread on the outside when frosting, run your cake scraper and offset spatula under hot water.