Make the Genoise Sponge Cake:

1. Preheat oven to 350°F (175°C). Grease and line the bottom of a round 8-inch cake pan.

2. In a stand mixer, beat eggs and sugar on high speed for 5–7 minutes until pale, thick, and tripled in volume.

3. Gently fold in sifted cake flour using a spatula, being careful not to deflate the mixture.

4. Mix milk, oil, and vanilla in a separate bowl. Add a scoop of the batter to the milk-oil mixture, stir to combine, then fold it back into the main batter.

5. Pour batter into the pan and bake for 25–30 minutes, or until a toothpick comes out clean. Cool completely, then slice into layers.

Make the Vietnamese Coffee Syrup:

1. Brew Vietnamese coffee using a phin filter or French press.

2. Stir together brewed coffee, water, and Kahlua. Set aside to cool.

Make the Mascarpone Layer:

1. In a bowl, whisk egg yolks and sugar over a double boiler until thickened and pale (about 5 minutes). Let cool.

2. In another bowl, whip heavy cream and vanilla until stiff peaks form.

3. In a third bowl, beat mascarpone until smooth. Add coffee/Kahlua and cooled egg mixture. Fold in whipped cream until combined.

Assemble the Cake:

1. Place one cake layer on a plate. Brush generously with coffee syrup.

2. Spread a thick layer of mascarpone cream on top.

3. Repeat with remaining layers.

4. Cover and refrigerate for at least 4 hours (preferably overnight) to set.

5. Dust with cocoa powder before serving.