This tiramisu cake is made with a coffee-infused vanilla cake, whipped mascarone frosting, and cocoa powder. It's lighter than the original dessert, but still perfectly rich and creamy.
Preheat oven to 350°F (175°C). Line a 9" x 13" x 2" baking pan with parchment paper. Butter and flour the paper and any exposed parts of the inside of the pan. (You can instead use a cooking spray with flour, like Baker's Joy or Pam for Baking.)
Whisk together the flour, sugar, baking powder, and salt in a large mixing bowl.
Add the butter, and mix with an electric mixer on medium-low speed until combined. The mixture will appear sandy.
Combine the milk and vanilla. Add to the batter, and mix on low speed until combined (about a minute).
Add one egg and mix, beginning on low speed and increasing to medium speed after a few seconds. Mix just until combined (about 30 seconds). Repeat with the remaining eggs.
Transfer the batter to the prepared pan and spread evenly. Gently tap the pan on the counter a few times to get rid of any large air pockets.
Bake 35 to 40 minutes, or until the cake is golden brown and a pick inserted into the center comes out clean.
Place the cake pan on a wire rack to begin cooling.
To make the coffee mixture:
Stir together the water, sugar, and espresso powder, stirring until the sugar dissolves. Stir in the liqueur. Set aside to cool.
To make the frosting:
Using an electric mixer on medium speed, beat the mascarpone, confectioners' sugar, and vanilla (or liqueur) until combined.
In a separate bowl, whip the cream with an electric mixer with a whisk attachment until stiff peaks form. Fold about a quarter of the whipped cream into the mascarpone mixture. Then gently fold in the remaining whipped cream.
To assemble:
After the cake has cooled but is still warm, either leave it in the pan or remove it from the pan onto a serving tray. Use a fork or a toothpick to poke holes over the top of the cake.
Brush the top of the cake with the coffee mixture. Make a few passes brushing it onto the cake, giving it a couple of minutes in between to let it soak up the mixture if needed. Try to use it all, but it's fine if you can't.
After the cake has finished cooling, spread the frosting over the top. Dust with cocoa powder.
Notes
To store: Keep the cake tightly covered in the refrigerator. Bring to room temperature before serving. It should keep in the refrigerator up to 5 days, although it will be at its best within a day or two.