Tall Marble Layer Cake with Chocolate Ganache

For the Cake

• Nonstick spray or butter, for the pans
• 3¾ cupsAll-Purpose Red Fife flour (443 g)
• 3 tspBaking powder
• 1½ tspSalt
• ¾ tspBaking soda
• 1 cup + 2 tbspUnsalted butter, room temperature (255 g)
• 2⅝ cupsGranulated sugar (525 g)
• 5Large eggs, room temperaturerounded up from 4.5 for a sturdier crumb in a taller cake
• 1/2 cupVegetable oil (120 g/120 ml)
• 1 tbspVanilla extract
• 1½ cupsFull-fat sour cream, room temperature (360 g)
• 1 cupWhole milk, room temperature, divided (about 248 g/ml)
• ¾ tspInstant espresso powder
• 6 tbspUnsweetened Dutch-process cocoa powder (32 g)

For the Chocolate Ganache Frosting

• 24 ozSemisweet chocolate, finely chopped (680 g)
• 3 cupsHeavy cream (720 ml)
• 1 tspVanilla extract
• PinchSalt

Directions

1. Preheat the oven to 350°F (177°C). Grease three 9-inch round cake pans, line the bottoms with parchment rounds, and grease the parchment.
2. In a medium bowl, whisk together the flour, baking powder, salt, and baking soda. Set aside.
3. In a large bowl, beat the butter and sugar together until light and fluffy, about 3 minutes. Add the eggs one at a time, then the oil and vanilla, beating well after each addition. Mix in the sour cream until just combined. With the mixer on low, add the flour mixture in two additions, alternating with 3/4 cup of the milk, mixing just until no streaks remain. The batter will be thick.
4. Scoop a little more than a third of the batter (about 4 1/2 cups) into a separate bowl. Warm the remaining milk until just warm to the touch and stir in the espresso powder. Pour it into the smaller bowl of batter, sift the cocoa powder over top, and whisk gently until combined.
5. Divide the vanilla and chocolate batters between the three prepared pans, dropping spoonfuls of each and alternating as you go. Drag a knife or skewer through each pan a few times to create a marbled swirl. Don't overmix, or the marbling will blur.
6. Bake for 26 to 30 minutes, until a toothpick inserted in the center comes out clean. Cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely before frosting.
7. Make the ganache. Place the chopped chocolate in a heatproof bowl. Heat the cream until it just begins to simmer, then pour it over the chocolate. Let sit for 2 to 3 minutes, then whisk until smooth. Stir in the vanilla and salt.
8. Let the ganache cool to room temperature, then refrigerate, stirring every 15 minutes, until thick enough to hold its shape, about 1 to 1½ hours.
9. Beat the thickened ganache with a mixer on medium-high for 1 to 2 minutes, until lightened in color and spreadable. Don't overbeat, or it can turn grainy.
10. Level the cooled cake layers if needed, then stack and fill with ganache between each layer. Frost the top and sides with the remaining ganache.