Combine cooled espresso, coffee liqueur, and 2 tablespoons sugar in a shallow dish, stirring until sugar dissolves.
In a large bowl, whisk egg yolks and ¾ cup sugar over a double boiler (or simmering water bath) for 8-10 minutes until thick, pale, and ribbony, reaching 160°F.
Remove from heat and whisk in mascarpone, vanilla, and salt until smooth and creamy with no lumps.
In a separate bowl, beat heavy cream to stiff peaks, then gently fold into the mascarpone mixture until fully incorporated.
Quickly dip each ladyfinger into the coffee mixture for 2-3 seconds per side (don't oversoak), then arrange in a single layer in the baking dish.
Spread half of the mascarpone cream evenly over the ladyfingers, smoothing with an offset spatula.
Repeat with another layer of dipped ladyfingers and the remaining mascarpone cream, smoothing the top.
Cover tightly with plastic wrap and refrigerate for at least 6 hours or overnight to set and allow flavors to meld.
Just before serving, dust generously with cocoa powder using a fine mesh sieve and garnish with chocolate shavings if desired.