Are custard pies funny?

"Dickens is able to go on being funny because he is in revolt against authority, and authority is always there to be laughed at. There is always room for one more custard pie."---Fifty Orwell Essays

I don't know if I have tasted a custard pie. What did Orwell want to say by refering to this sort of food? Are custard pies funny?

I guess that the following is not related to my question:
https://www.sffchronicles.com/threads/532710/