Set up a double boiler by filling a medium-sized saucepan with 1-2” (about 4cm) of water. Place a medium-sized heatproof bowl on top, making sure the bottom does not touch the water. Remove the bowl, and turn the heat to medium-low to bring the water to a simmer.

Meanwhile, place egg yolks in the bowl (off heat) and whisk vigorously for about 60 seconds.

Add sugar 1 Tablespoon at a time, whisking vigorously for 30-60 seconds between each addition.

Add salt and whisk to combine.

Combine rum and vanilla extract and gradually whisk the rum/vanilla mixture into the egg yolk mixture. Whisk vigorously for at least another minute, sugar should be dissolving (but may not be completely dissolved, this is OK).

Place bowl over saucepan of simmering water and whisk constantly until sugar has completely dissolved and temperature reaches 160F (71C), this could take around 5-10 minutes or even longer. Be sure to whisk in anything that sticks to the sides of the bowl to ensure everything is uniform. When finished, mixture will be thicker than pudding in consistency.

Pour/spoon mixture into a separate, heatproof bowl to stop it from cooking further and allow to cool for 10 minutes, then press parchment paper against the surface and place in the refrigerator to chill while you prepare the rest of the cake.

Preheat your oven to 350F (175C) and prepare three 8-inch round cake pans by greasing and flouring the sides and lining the bottoms with parchment paper. Be sure to shake out any excess flour from the pans, set aside.

In a large mixing bowl, use an electric mixer to beat butter until creamy.

Add oil and sugar and beat until well-combined.

Add vanilla extract and stir to combine, be sure to scrape the sides and bottom of the bowl with a spatula to combine all ingredients.

In a separate, medium-sized bowl, whisk together flour, baking powder, and salt.

With your mixer on medium speed, alternate between adding the flour mixture and the milk to the butter mixture. You should start and end with the flour mixture, stirring between each addition to completely incorporate all ingredients before adding the next. Set aside.

In a separate clean, dry, large mixing bowl, use an electric mixer (be sure to use clean, dry beaters!) to beat your egg whites, starting at low speed and increasing to high speed, whisking until stiff peaks form.

Using a spatula, gently fold the egg whites into your batter. Be sure to scrape the sides and bottom of the bowl with a spatula, and only fold in until just combined.

Evenly divide cake batter into your prepared pans, each pan should have around 450g of batter.

Bake in preheated 350F (175C) oven for 22-25 minutes, until cakes are a light golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs.

Allow cakes to cool in cake pans for 10 minutes, then run a knife around the inside rim of the pan to loosen cakes and carefully invert onto a cooling rack. Cool completely before assembling.

In a small saucepan over medium/low heat, combine coffee and sugar and stir until sugar is completely dissolved.

Remove from heat and add rum, stir to combine. Set aside while you prepare your frosting.

In a large bowl, use an electric mixer to beat heavy cream and ½ cup (62g) of powdered sugar until you just hit stiff peaks. Set aside.

In a separate large bowl, add mascarpone cheese, zabaglione, and remaining ½ cup (62g) powdered sugar. Use a spatula to very gently fold ingredients together until thoroughly combined. You want to stir as little as possible while still completely combining ingredients, as too much stirring can cause the cheese to curdle.

Add whipped cream to the cheese mixture and use a spatula to very gently fold until thoroughly combined, while still trying to stir as little as possible.

Once cakes are completely cool you may begin to assemble. Level cakes if necessary.

Top with a thick, even layer of frosting. Repeat with the next two cake layers, topping the last layer with a thick layer of frosting.

Frost the sides of the cake with a thin, smooth, semi-naked covering of frosting. Use the remaining frosting to make dollops on the top of the cake (I used an Ateco 848 tip).

Gently sift cocoa powder evenly over the top of the cake. Refrigerate, covered, for at least an hour or two before slicing and serving.