Dissolve Espresso: In a small bowl, dissolve the instant espresso powder in the hot water. Stir in the vanilla extract and coffee liqueur (if using). Set aside to cool completely.

Whip the Cream: In a large, chilled bowl, use an electric mixer to beat the cold heavy cream on high speed until stiff peaks form.

Create the Base: In a separate bowl, whisk together the sweetened condensed milk and the cooled espresso mixture. Gently fold this mixture into the whipped cream using a spatula until it is just combined. Be careful not to deflate the cream.

Add Flavor and Freeze: Pour half of the gelato mixture into a 9x5-inch loaf pan or a freezer-safe container. Sprinkle half of the cocoa powder and half of the crushed ladyfinger cookies over the top. Add the remaining gelato mixture, and sprinkle with the rest of the cocoa and ladyfingers.

Freeze: Cover the pan tightly with plastic wrap and freeze for at least 6 hours, or preferably overnight, until firm. Before serving, let the gelato sit on the counter for a few minutes to soften slightly.