Make Crust: Butter the sides only (not the bottom) of a 9-inch spring-form pan (about 2 1/2 to 3 inches deep). Grind the Amaretti very fine in a food processor or blender. Mix with sugar in a mixing bowl. Melt the chocolate and butter in the top of a double boiler, stirring occasionally. Add the melted mixture to the Amaretti crumbs and sugar and mix thoroughly. (Don't wash the double boiler; you'll be using it again in a minute.) Turn the mixture into the prepared pan. With your fingers, distribute it evenly over the bottom and press it down into a very firm, compact layer. Refrigerate
while you prepare the filling.
Make Filling: Adjust rack 1/3 up from the bottom of the oven and preheat to 350 degrees F. Partially melt chocolate in the top of a double boiler, then uncover and stir until completely melted. Remove the top of the double boiler and set aside to cool. Break the Amaretti coarsely into a bowl and set aside. Cut the almond paste into small pieces, and beat on low speed with an electric mixer, while gradually adding the Amaretto liqueur. Beat until thoroughly mixed and set aside. Beat the cream cheese with an electric mixer until smooth. Add the sugar and beat until smooth again. Add the almond paste- Amaretto mixture and beat until thoroughly mixed. Add the melted chocolate and beat well again. Add the eggs one at a time, beating at low speed until they are incorporated after each addition. Add the heavy cream and beat until smooth. Add the coarsely broken Amaretti and stir gently only to mix. Turn into the prepared pan, pouring the mixture over the bottom crust. Rotate the pan gently to level the batter. (Don't worry if the mixture comes almost to the top; it won't run over.) Bake 45 minutes. It will seem soft and not done, but don't bake any more; it will become firm when chilled. The top of the cake is supposed to look bumpy because of the large chunks of Amaretti. Let cool completely at room temperature, then carefully remove the sides of the pan and refrigerate the cake (still on the bottom of the pan) for 4 to 6 hours, or overnight.