Place chocolate in a food processor. Cover and process until finely chopped. Add tofu, 1/4 cup espresso, sugar, lemon juice, and salt. Cover and process until nearly smooth.
Place a cake piece in the bottom of each of 12 shot glasses or demitasse cups, pressing lightly. Drizzle each with about 1/2 teaspoon espresso or liqueur. Spoon about 1 tablespoon of the tofu mixture over each cake piece in the glasses. Top each with remaining cake pieces. Spoon remaining tofu mixture over each.
Place glasses on a tray. Cover with plastic wrap. Chill for 30 minutes or up to 24 hours.
To serve, lightly sift cocoa powder over mixture in glasses and top each with an espresso bean.