I've always used the pie. I guess Richter doesn't like custard 
The first time that I've won against him I didnt knew about some secret areas, so I couldnt use the pie even if I wanted, I've used the javelin in max level (also I didnt beat any of the last portrait levels, so no bonus against him, now imagine my frustration when I discovered that you can find a dark whip and a holy armor beating these areas lol. Even so its was awesome to me that I defeated him this way).
This time I tried using the pie but even so, shuriken deals even more damage and can kill him faster and easier (discovered this in a random internet search)