Place 2 cups milk in a medium, heavy saucepan; bring to a boil. Combine sugar, cornstarch, and salt in a large bowl, stirring well with a whisk. Combine remaining 1/2 cup milk and egg yolks, stirring well with a whisk. Add egg yolk mixture to sugar mixture, stirring well. Gradually add half of hot milk to egg yolk mixture, stirring constantly with a whisk. Return milk mixture to pan; bring to a boil. Reduce heat, and simmer 1 minute or until thick, stirring constantly. Remove from heat. Add butter, vanilla, and chocolate, stirring until melted.

Spoon pudding into a bowl. Place bowl in a large ice-filled bowl for 15 minutes or until pudding is cool, stirring occasionally. Cover surface of pudding with plastic wrap; chill.

Combine the chocolate and water in a saucepan. Place in a skillet of barely simmering water and heat, stirring as necessary, until chocolate melts.

Meanwhile, put the egg yokes and sugar in a bowl of an electric mixer (or another heatproof bowl). Add the creme de cacao and set bowl in another skillet of barely simmering water. Beat vigorously with a wire whisk until the sauce becomes thick, like a stiff custard. Remove from the hot water and let cool briefly.

Let the melted chocolate cool slightly (if it is too hot when added to the sauce, it will tend to overcook the eggs). Add the chocolate to the sauce and fold it in with a rubber spatula. Beat in the rum.

Whip the cream until stiff. Fold in the chocolate mixture.

Spoon the chocolate filing into the bake tart shell. Cool briefly, then chill in the refrigerator or freezer, depending on the time available.

Garnish with additional whipped cream, if desired.

Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, cocoa, baking soda, and salt, stirring well with a whisk. Place shortening in a large mixing bowl; beat with a heavy-duty mixer at medium speed until light and fluffy. Gradually add the granulated sugar, 1 tablespoon at a time, beating until well blended. Add vanilla and egg white; beat well. Add flour mixture; beat until well blended.

Turn dough out onto wax paper; shape into a 6-inch log. Wrap log in wax paper. Freeze 2 hours or until very firm.

Cut log into 24 (1/4-inch) slices, and place slices 1 inch apart on baking sheets coated with cooking spray. Bake at 350º for 10 minutes or until set. Remove from pans; cool completely on wire racks.

Combine powdered sugar and milk in a medium bowl; stir well with a whisk until smooth. Spoon into a small zip-top plastic bag; seal. Snip a tiny hole in 1 corner of bag. Working with 1 cookie at a time, pipe 3 concentric circles onto each cookie. Starting at center circle, pull a wooden pick through other circles at regular intervals to create a "web."