The Mystery of the Soup Pie
So, here's something that happened here in the kitchen which has me puzzled. Maybe someone in the community can help figure out what went wrong.
First the recipe used, for chocolate pie
1 1/4 cups sugar
1/2 cup cocoa
1/3 cup cornstarch
1/4 teaspoon salt
3 cups milk
3 egg yolks
3 tablespoons margarine
1 1/2 teaspoon vanilla
1 baked pie shell
Combine sugar, cocoa, cornstarch, and salt into a heavy saucepan. Mix well to remove lumps, then slowly add milk, stirring until well-blended. Cook over medium heat, stirring constantly, until mixture thickens and comes to a boil. Boil 1 minute, stirring constantly. Remove from heat to let cool Beat yolks until thick, gradually add about 1/4 of chocolate mixture into yolks. Add to remaining cocoa mixture, stirring constantly. Cook over medium heat 2 minutes, remove from heat, and stir in margarine and vanilla. Pour immediately into pie shell and let set at least 3 hours in the refrigerator.
OK, here's the thing: the chocolate filling never set. After four hours in the fridge, it was like chocolate soup, thin enough to pour! Now, the recipe is an old one my mom uses and has used for years, and she was the one actually making the pie. She has had a lot of experience with this recipe, they usually turn out fine, and my mom is a professional cook who worked in kitchens her whole life. I questioned her about the pie, making sure she didn't overlook anything (she is 67 years old and does occasionally forget stuff). So we're mystified about what went wrong.
Does anyone have any idea why the chocolate filling never set and went from thick liquid to solid as it cooled and chilled?