Preheat the oven to 180°C (350°F) and line a 40 x 25 cm pan with parchment paper.

Dissolve 10g coffee powder in 45g warm milk and set aside.

Separate 3 eggs into yolks and whites; mix 10g sugar with the yolks, then add 45g vegetable oil and the coffee mixture.

Sift 80g cake flour into the yolk mixture and stir until smooth.

In a separate bowl, whisk egg whites with a pinch of salt until foamy using an electric mixer with a whisk attachment, then gradually add 60g sugar in three batches until stiff peaks form.

Fold egg whites into the yolk mixture in three batches, gently incorporating until smooth.

Pour the batter into the prepared pan and bake for 12-15 minutes at 180°C. Cool the cake completely.

Mix 1 tbsp hot water with 2 tsp coffee powder, then let it cool.

Whisk 40g sugar with 100g mascarpone cheese, then add 250g cold heavy cream and whip until soft peaks form.

Stir in the cooled coffee mixture and whisk gently until fully combined.

Cut the cooled cake into 3 equal layers.

Spread or pipe coffee cream onto the first layer, smooth it out, and add the second layer.

Repeat the process with the third layer, then cover the top with the remaining cream.

Chill for at least 3 hours, or overnight, to set.

Trim edges for a neat look and slice into 5 portions.

Decorate with cocoa powder and optional chopped hazelnuts.