For the pudding, stir together the milk and sugar in a small saucepan and place it over medium-low heat. Meanwhile, in a small bowl, whisk together the espresso, coffee liqueur, cornstarch and cocoa powder. When the milk begins to bubble around the edges of the pan, whisk in the espresso mixture. Continue to whisk until the pudding comes to a bubble and thickens, about 3 minutes.  

Place a fine-mesh strainer over a bowl. Pour the warm pudding through the sieve to remove any lumps. Divide the pudding into 4 martini glasses or small cups. Cover each with plastic wrap, making sure the wrap touches the pudding so it doesn't form a skin. Refrigerate for at least 4 hours before serving. 

To make the topping, in a large bowl, whisk together the instant espresso powder, sugar and water for 2 minutes, or until the mixture becomes thick and frothy. Set aside.  

To serve, dollop each serving of pudding with the topping and dust with cocoa powder.