For the crust, in a mixing bowl combine crushed wafers and melted butter. Press mixture evenly onto the bottom and 2 inches up the sides of an ungreased 8-inch springform pan. Place the pan on a baking sheet. Chill until needed.

In a small saucepan combine the chocolate, water, and instant espresso. Cook and stir over low heat until chocolate starts to melt. Remove from heat. Stir until smooth. Stir in liqueur or water; cool.

In a large mixer bowl beat cream cheese, sugar, flour, and vanilla with an electric mixer on medium speed until smooth. Add eggs all at once, beating on low speed just until mixed. Do not over beat.

Reserve 2 cups of the cream cheese mixture; cover and chill. Stir cooled chocolate mixture into the remaining cream cheese mixture, stirring just until combined. Pour chocolate mixture into crust.

Bake in 350 degree F oven for 30 minutes or until sides are set (center will be soft-set). Remove reserved mixture from refrigerator 10 minutes before needed. Gently pull out oven rack just enough to reach the inside of the pan. Carefully pour reserved mixture in a ring over the outside edge of the chocolate mixture (where chocolate mixture is set). Gently spread evenly over entire surface.

Bake cheesecake for 20 to 25 minutes more or until center appears nearly set when gently shaken. Cool for 10 minutes on a wire rack. Loosen sides of the cheesecake from the pan. Cool for 30 minutes. Remove sides of pan. Cool completely.

Chill cheesecake for 4 to 24 hours before serving. Store any remaining cheesecake, covered, in the refrigerator for up to 3 days. Makes 12 servings.

Chill cheesecake, covered, for 4 to 24 hours ahead. Or, to freeze, place cooled cheesecake, uncovered, in the freezer for 1 hour or until firm. Remove bottom of pan. Transfer cheesecake to a large freezer bag or container. Seal, label, and freeze for up to 1 month. To serve, transfer cheesecake to a platter and loosely cover. Thaw for 24 hours in the refrigerator.