Make the caramel: Heat sugar in a saucepan until melted and golden brown.
Slowly whisk in espresso, cream, butter, and salt until smooth. Let it cool slightly.
Whip mascarpone, heavy cream, powdered sugar, and vanilla until thick and fluffy.
In a shallow dish, combine espresso and coffee liqueur.
Dip each ladyfinger quickly into the espresso mixture—don’t soak them into mush.
Layer half the ladyfingers in the baking dish.
Spread half the mascarpone mixture over the ladyfingers.
Drizzle half of the coffee caramel over the mascarpone layer.
Repeat with another layer of ladyfingers, mascarpone, and caramel.
Smooth the top and dust generously with cocoa powder.
Cover and refrigerate for at least 4 hours—overnight is best.
Slice, serve, and watch it disappear.