Brew 150 ml / 2/3 cup espresso, stir in 30 ml / 2 tbsp coffee liqueur, and pour it into a shallow dish about 20 cm / 8 inches wide. Let it cool to room temperature, about 10 minutes, while you make the filling.

In a 3-quart / 2.8 L bowl, beat the cold heavy cream, powdered sugar, vanilla, and salt with a hand mixer on medium-high for 2 to 3 minutes, until the peaks hold their shape when you lift the beaters. In a 2-quart / 1.9 L bowl, stir the cold mascarpone with a spatula for 30 seconds until loose and smooth. Fold in a third of the whipped cream, then fold in the rest until no streaks remain.

Working one at a time, dip a ladyfinger into the espresso for 1 to 2 seconds per side, then snap it in half. Press 3 halves into the bottom of a 240 ml / 8-oz glass. Spoon in about 50 ml / 3 1/2 tbsp of the cream, smooth it, and dust with about 1/2 tsp cocoa through a fine-mesh sieve. Add 3 more dipped halves and top with the remaining cream, dividing it evenly. Repeat to fill all 6 glasses.

Cover each glass with plastic wrap or a lid and refrigerate for at least 4 hours, ideally overnight, until the cream is set and the ladyfingers have softened into a cake-like layer.

Just before serving, dust the remaining cocoa (about 1 tbsp) over the tops through the sieve and scatter the shaved chocolate. Serve cold with small spoons.