Combine cooled espresso, sugar, and vanilla in a wide shallow dish. Stir until sugar dissolves. Set aside.

Fill a medium saucepan with 5cm of water and bring to a gentle simmer. In a large heatproof bowl, combine egg yolks, 80g sugar, and 3 tablespoons water. Set over the simmering water without the bowl touching the water. Whisk continuously for 7 to 10 minutes until pale, tripled in volume, and holding a 4 to 5-second ribbon. Target temperature: 71°C (160°F). Remove from heat and whisk over ice water until cool.

Beat mascarpone until completely smooth. Fold cooled sabayon into mascarpone in three additions using gentle, broad strokes.

Whip cold heavy cream with 40g sugar to stiff peaks. Fold into the mascarpone mixture in three additions. Set aside.

Line a 9-inch springform pan with parchment on the base and sides. Dip ladyfingers one at a time in the espresso soak for exactly 1 second per side. Arrange in a tight single layer covering the pan base.

Spread half the mascarpone cream evenly over the first ladyfinger layer. Dip and arrange a second ladyfinger layer on top. Spread the remaining cream in an even, flat-surfaced layer reaching the pan edges.

Sift cocoa powder evenly over the entire cream surface through a fine-mesh sieve to form a uniform blanket. Cover tightly with plastic wrap and refrigerate for 8 hours or overnight.

To serve, release the springform, slide out the parchment, and serve cold, slicing with a knife dipped in hot water and wiped clean between cuts.