Whisk the mascarpone cheese on medium speed for 30-60 seconds until creamy. Scrape the bowl and set aside.

In a separate heat-proof bowl, add the egg yolks and ⅔ cup sugar. Create a double boiler and whisk on medium-high speed for exactly 2 minutes, then remove from heat.

Pour the egg yolk and sugar mixture onto the mascarpone cheese. Add salt and vanilla, and whisk on medium speed just until combined.

In a separate bowl, whip the cold heavy cream until it reaches medium-stiff peaks. Fold the whipped cream gently into the mascarpone mixture in 2-3 additions.

Pour the coffee into a wide bowl. Dip each ladyfinger quickly into the coffee and layer them at the bottom of an 8x9.5" rectangular dish.

Spread half of the mascarpone cream evenly over the ladyfingers.

Repeat with another layer of soaked ladyfingers and top with the remaining mascarpone cream.

Cover and refrigerate for at least 6 hours, or ideally overnight.

When ready to serve, sift cocoa powder on top of the tiramisu, cut into slices, and serve.