In the bowl of a stand mixer fitted with the whisk attachment, beat the egg yolks on medium-high speed until fluffy and light yellow, about 2 minutes. With the mixer running, slowly stream in the granulated sugar and continue to beat until the mixture is pale and has tripled in volume, about 5 minutes.
With the mixer on low, add the mascarpone, vanilla, and salt. Increase the speed to high and whip until smooth and fluffy, about 1 minute.
Slowly pour in the heavy cream and whip until soft peaks form, about 1 minute.
In a shallow bowl, whisk together the espresso and cocoa powder until dissolved.
Working one at a time, quickly dip each ladyfinger into the espresso mixture — just long enough for the cookie to absorb the liquid without becoming soggy.
Arrange a layer of espresso-dipped ladyfingers in the bottom of a 9×13-inch baking dish. Spread half of the mascarpone mixture over the top and smooth into an even layer. Dust with cocoa powder.
Repeat with another layer of espresso-dipped ladyfingers, the remaining mascarpone mixture, and a final dusting of cocoa powder.
Cover and refrigerate for at least 4 hours, or overnight. This step allows the cream to set and the flavors to meld. Serve chilled.