Combine butter, sugar and cocoa powder. Stir in crumbs. Press evenly over bottom of greased 23 cm springform pan and bake at 180ºC or 10 minutes. Cool pan and grease sides.
Beat cream cheese until smooth. Gradually beat in sugar. Beat in eggs, one at a time. Blend in Bailey s. Pour about one third mixture into a bowl and stir in melted chocolate. Pour half of plain mixture into prepared pan. Drizzle with half the chocolate mixture. Repeat layers. Make a marbled design by gently swirling batter with a knife. Bake 10 minutes at 450, then 55 minutes at 250.