To make the trifle: Using an electric mixer, beat the mascarpone, melted chocolate, powdered sugar, and espresso powder in a large bowl until smooth and fluffy.
Divide half of the panettone cubes among 6 wine glasses or old-fashioned glasses. Sprinkle half of the coffee liqueur over the panettone. Top with half of the mascarpone mixture. Repeat layering with the remaining panettone, liqueur, and mascarpone mixture. (The trifles can be prepared 1 day ahead, covered and refrigerated. Let come to room temperature before serving.)
To serve, sprinkle with the chocolate shavings. Serve immediately.