In a food processor or blender, whirl chocolate until finely chopped. Pour into a bowl. Put eggs and yolks in the processor or blender.
In a 4-cup glass measure, heat whipping cream in a microwave oven (see Notes) at full power (100%) until cream boils, 3 to 5 minutes.
With processor or blender on high speed, add boiling cream to egg. Check temperature of mixture with an instant-read thermometer; if below 160°, pour mixture back into glass measure and reheat in microwave oven at full power until it reaches 160°, stirring and checking at 15-second intervals.
Combine hot cream mixture, chopped chocolate, and liqueur in blender or processor (or whisk the ingredients together in a large bowl); whirl until smooth, about 1 minute.
Pour chocolate mixture into 8 ramekins or glasses (1/2-cup size). Chill until softly set, 30 to 45 minutes. If making ahead, cover and chill up to 1 day. For creamiest texture, let desserts stand at room temperature about 30 minutes before eating.
Spoon 1 tbsp. wafer crumbs onto each pot de crème. Insert a Tombstone Cookie into each serving.
Note: Nutritional analysis is per serving with 1 Tombstone Cookie.