Fill the saucepan with a few centimetres of water and bring it to a gentle simmer to make a double boiler.

Whisk the 4 egg yolks with 90 g caster sugar in the heatproof mixing bowl set over the simmering water.

Continue whisking until the sugar dissolves and the yolk mixture becomes pale, thick, and voluminous.

Remove the bowl from the heat and whisk in 300 g mascarpone with 1 teaspoon vanilla extract until smooth.

Refrigerate the mascarpone mixture for a few minutes if it feels warm, until cooled.

Whip 120 ml whipping cream with 35 g icing sugar until stiff peaks form.

Fold the whipped cream into the mascarpone mixture gently until the cream is evenly combined.

Pour the 240 ml strong coffee into the shallow bowl and briefly dip half of the ladyfinger biscuits into it.

Arrange the soaked ladyfinger biscuits in a single layer in the serving dish.

Spread half of the mascarpone cream over the biscuits in an even layer.

Dust the cream generously with about 5 g cocoa powder using the fine-mesh sieve.

Dip the remaining ladyfinger biscuits in the coffee and arrange them over the cocoa-dusted cream.

Spread the remaining mascarpone cream over the second biscuit layer until smooth.

Dust the top generously with the remaining cocoa powder.

Refrigerate the tiramisu for at least 360 minutes before slicing and serving chilled.