Tuxedo Cake Recipe

Preheat the oven to 325F/163C convection (or 300F/149C conventional) and grease and line four 6 inch (15cm) round pans with baking spray and parchment paper.*
In a large bowl, whisk together the flour, sugar, cocoa powders, baking powder and salt until they're well combined.
2 cups (240g) all-purpose flour spooned and leveled, 2 cups (400g) granulated sugar, 1/2 cup (40g) dutch-process cocoa powder spooned and leveled, 1/2 cup (40g) black cocoa powder spooned and leveled, 1 Tbsp (10g) baking powder, ½ tsp salt
In a separate large bowl, whisk together the oil, eggs, coffee and milk, until they're well combined.
3/4 cup (177mL) vegetable or canola oil, 2 large eggs room temperature, 3/4 cup (177mL) coffee, 3/4 cup (177mL) milk room temperature
Sift the dry ingredients over the wet ingredients and then whisk together until the batter is completely smooth.
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.
Flip the cake over onto a tea towel and allow it to cool to room temperature.

When the cakes are almost done baking, make the white cake.
In a medium bowl, whisk together the flour, baking powder and salt until they're evenly distributed.
3/4 cup (90g) cups all-purpose flour spooned and leveled, 1 tsp (4g) baking powder, 1/4 tsp salt
Whisk together the oil and the granulated sugar in a large bowl until they're smooth.
1/4 cup (60mL) vegetable oil, 1/2 cup (100g) granulated sugar
Add the egg whites and whisk aggressively for 1-2 minutes (or use an electric mixer), until the color lightens a little.
2 large egg whites room temperature
Add the sour cream and vanilla extract and whisk just until combined.
1/4 cup (56g) sour cream room temperature, 1 tsp vanilla extract
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.
1/4 cup (60mL) heavy whipping cream room temperature
Prepare one more pan and pour the batter into one 6 inch round pan (or two pans - the total weight is 14 oz so you can do two pans of 7oz) 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.
Flip the cake over onto a wire rack or tea towel and allow the cakes to cool completely before slicing in half.

Place the white chocolate into a large bowl and the dark chocolate into a separate large bowl.
3 cups (18oz) dark chocolate chips, 3 cups (18oz) white chocolate chips
Place the heavy whipping cream into a small saucepan and heat over medium heat until it comes to a heavy simmer (bubbling all around the edge).
2 cup (16oz) heavy whipping cream, 1 cup (8oz) heavy whipping cream
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.
Use a rubber spatula to gently stir the ganaches until they're completely smooth.
Cover again and allow them to cool completely to room temperature. (or just slightly chilled) - See notes**
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.

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).
Place a layer of white cake next, topped with a layer of dark chocolate ganache.
Next place a layer of chocolate cake, then white chocolate ganache and then another chocolate cake.
Now spread a layer of the chocolate ganache and the second white cake.
Last, spread a layer white chocolate ganache followed by the last chocolate cake.

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