Heat 2/3 cup cream in a large microwave safe bowl until steaming. (Time will vary depending on wattage of oven.) Add chips; whisk until smooth. Slowly whisk in remaining cream. Chill 15 minutes.
Beat mixture in step one with mixer just until soft peaks form. Arrange 3 crackers, side by side, long edges touching on a serving plate. Spread evenly with 1/2 cup cream mixture. Repeat for 4 more layers; add 1 more layer of crackers. Chill 1 hour. Chill remaining cream.
Spread top and sides of cake with remaining cream. Chill 4 hours or up to 2 days.
Decorate with peanut butter chips, if desired. Slice with serrated knife using a sawing motion.