I made pastry cream for the first time in my double boiler. The next day it was watery. I cooked it till it was thick, but maybe I didn't get it thick enough. I did not bring it to a boil. Was I suppose to bring it to a boil?
I've never understood making pastry cream in a double boiler. It needs to come to a boil so that the starch is cooked and comes to the proper thickening point. Also, to get rid of the starch taste. Pastry cream will start to have water separation after a few days, but shouldn't that soon. I would say it was cooked enough.
You must bring pastry cream to a boil for at least 1 minute. There are enzymes in the egg yolks that destroy the network of starch strands established during the cooking process. Bringing the mixture to a boiling point for 1 minute neutralizes those enzymes and your pastry cream will remain thick for days.
Cooking it in a double boiler will prevent that from happening.