Place the cubes of chocolate cake or cookie crumbles in the bottom of six to eight 12-ounce champagne coupes or medium-size stemmed wine glasses. Brush with the cacao rum liqueur.

In a small saucepan, sift the cocoa powder, salt, sugar and cornstarch into the half-and-half and then begin to heat. Heat, stirring, until the mixture reaches 180 degrees F. Add the chocolate and vanilla extract and cook, stirring, for one full minute. Pass the pudding through a fine-mesh sieve and then pour directly into the champagne coupes. Place plastic wrap on the surface of the pudding and set aside to cool for 30 minutes to 1 hour.