In a large bowl, beat the egg yolks and 6 tablespoons of the sugar with a hand mixer until frothy and the sugar is no longer visible.
Add the mascarpone and beat on low speed just until smooth. Do not overbeat.
In a clean bowl with clean beaters, beat the egg whites until foamy. Add the remaining 6 tablespoons of sugar, a spoonful at a time, and beat until soft peaks form.
Fold half of the egg whites into the mascarpone mixture, then gently fold in the rest until no streaks remain.
Pour the espresso into a shallow bowl. Spoon a thin layer of the mascarpone cream into the bottom of each glass.
Dip a ladyfinger into the espresso for about 1 second per side. Break off about a quarter to a third so it lies flat, and place it over the cream. Save the broken pieces. Repeat to cover the cream in each glass.
Spoon a layer of cream over the ladyfingers. Add a second layer of dipped ladyfingers, breaking them to fit, and top with another layer of cream.
Dip the saved ladyfinger pieces and arrange them as the third layer. Top with the remaining cream, dividing it evenly among the glasses.
Cover and refrigerate for at least 3 hours.
Just before serving, dust the tops with cocoa powder through a fine-mesh sieve and garnish each glass with 3 espresso beans.