I piped the mascarpone filling on the top for decoration and dusted it with Dutch processed cocoa powder. Don’t try and substitute with regular cocoa powder – it’s bitter.
The only special equipment you need for this particular cake is an 11 x 17 pan, acetate rings, and a square cake ring. Let’s get started!!
Sponge Cake Adapted from The Sono Baking Company Cookbook
3/4 cup cake flour
1/2 cup cornstarch
4 large eggs, room temperature
4 large egg yolks, room temperature
2/3 cup sugar
1 teaspoon coarse kosher salt
1 Tablespoon vanilla
1 cup canola oil
Preheat the oven to 375 degrees. Spray an 11 x 17 inch pan with nonstick spray, line with parchment, and spray again. Set aside.
In small bowl, sift together the flour and cornstarch – set aside.
In the bowl of a Kitchenaid mixer, beat the whole eggs, egg yolks, sugar, salt and vanilla (with the whisk attachment) on high speed for 8 minutes. The mixture should be thick, pale yellow, and fluffy.
Remove the bowl and fold in the flour mixture until it has been completely incorporated. Continue to fold – even if you think you’ve combined all of it because the cornstarch has a tendency to stick to the bowl, and your cake will be ruined if all of the flour isn’t incorporated.
Once you’re sure all the flour has been folded in, slowly add in the oil while continuing to fold. It is helpful to have another person slowly drizzle the oil for you while you fold the batter, if possible.
Gently pour the batter into the prepared pan and bake for 10-15 minutes. To test the cake, stick the center of the cake with a toothpick and make sure that there is no batter on it. Remove the cake from the oven and let set for 2 minutes.
Then carefully turn the cake over onto a wire rack to cool completely. Don’t wait too long to do this because the hot pan it’s resting in may make the cake collapse. Let it cool for 30 minutes to an hour on the wire rack. When it feels cool to the touch it’s ready for the next step.
Mascarpone Custard Adapted from Everyday Occasions
4 cups heavy cream
1 2/3 cups granulated sugar
10 large egg yolks
6 Tablespoons cornstarch
8 Tablespoons of cold unsalted butter, cut into Tablespoons
1/2 teaspoon vanilla extract
2 (8 ounce) tubs of mascarpone cheese
Crack the egg yolks into a large glass (heat-proof) bowl and set aside. In a medium bowl, place the chunks of butter and vanilla and set a fine mesh sieve on top (I have some similar to these); set aside.
In a medium pot, whisk together the sugar with the cornstarch to break up any lumps. Then add the heavy cream and salt and whisk constantly over medium heat (about 5 on a gas burner) until thick and bubbly. Continue whisking for 1 minute.
Slowly, whisk about 1/2 of the hot cream into the egg yolks whisking vigorously to prevent the egg yolks from scrambling. Then slowly whisk in another 1/2 cup of hot cream.
Then place the remaining pot of hot cream back on the stove and vigorously whisk the egg yolk mixture back into the hot cream and bring it to a boil. Cook for 1 minute.
Take the cream/egg mixture off the heat and pour it through the sieve. When all of the custard has been pushed through the sieve, whisk constantly to incorporate the butter and vanilla into the hot cream mixture.
Pour the hot custard into a heat-proof bowl and let it set at room temperature for about 30 minutes to cool. Once it has cooled enough to move, place a paper towel on top of the bowl and place in the refrigerator to continue to cool.
Once the custard is cool, about 30-45 minutes, beat in the tubs of mascarpone cheese. The custard is ready to be spread and piped onto the tiramisu.
*This custard will be shiny, thick, and spreadable the first day. However, on the second day it will thickened so much that you can scoop it. Don’t worry, it’s crazy delicious and great on cream puffs because it’ll stay in place!
**If the custard “breaks” and separates on you, try processing it in a food processor or using an immersion blender if you have one. It should come together completely.
Now you’ll need 1 cup of espresso.
Use the square cake mold to cut the cake into two pieces. Then wash the mold. Line the mold with an acetate ring. Then place in layer of the sponge cake.
Brush the top of the sponge cake with espresso. Spoon on about 1/4 to 1/2 inch layer of custard cream. Top with the next layer of sponge cake, brush the cake with espresso, top with a layer of custard cream. Then fill a piping bag with the remaining custard and pipe the top. Dust with Dutch processed cocoa powder. Refrigerate for at least 3 hours, or overnight.
Remove the mold and acetate before serving. Keep covered in the refrigerator for 3-4 days.