Begin by preheating your oven to 325°F. Prepare three 6-inch cake pans (or two 9-inch pans if preferred) by greasing and flouring them thoroughly. Set aside for later use.

In a large mixing bowl with a whisk attachment, cream the softened butter and vegetable oil together until they are well blended into a smooth, cohesive mixture. This process will take around 3 minutes. It’s essential to ensure the butter is at room temperature for this to work.

Gradually add the granulated sugar to the butter and oil blend, mixing on high speed until the result is light and airy with a pale yellow hue, about 3 more minutes.

Incorporate the eggs one at a time, ensuring to scrape down the sides of the bowl after each addition to keep the batter smooth. Add the vanilla extract and mix well.

For the next 3 minutes, continue beating the mixture on high speed to incorporate as much air as possible for a fluffier cake.

In another bowl, sift together the cake flour, baking powder, and salt. Alternately add the dry mixture and buttermilk into the wet batter in four portions, starting with the buttermilk and finishing with the dry ingredients. Take care not to over-mix; a few small lumps in the batter are fine.

Evenly distribute the batter into the prepared cake pans and bake for 30 minutes, or until the cakes turn golden and spring back when lightly pressed. Keep an eye on them as baking times may vary depending on your oven. Once baked, transfer the cakes to a cooling rack to cool completely.

While the cakes cool, brew your coffee and stir in the sugar while it’s still hot, ensuring the sugar fully dissolves.

To prepare the mascarpone frosting, combine the mascarpone, powdered sugar, and vanilla extract in a stand mixer using the whisk attachment. Beat on medium speed for about a minute until the mixture is light and fluffy.

After scraping down the sides of the bowl, switch the mixer to medium-low speed and gradually pour in the chilled heavy cream. Continue mixing until everything is well combined and fluffy, which should take about 2 minutes. Be careful not to overwhip as this can cause the frosting to split. Once done, transfer the frosting to a piping bag fitted with a large round tip.

Assemble the cake by placing the first layer on a serving plate or cake stand. Generously brush the top with the coffee syrup using a pastry brush, allowing it to soak into the cake.

Pipe a layer of frosting on top, smoothing it out with an offset spatula if necessary. Repeat this process with the remaining cake layers, making sure each is soaked with the coffee syrup and frosted.

Frost the top and sides of the cake with the remaining frosting. If you wish to decorate, reserve some frosting for piping around the top edge of the cake. Finally, dust the top with cocoa powder.