Over the weekend, when I made Martha Stewart's Summer fruit cream pie, something went horribly wrong. As you can tell by the picture, the custard would not set! The recipe seemed simple enough; it's a graham cracker crust filled with cinnamon-berry custard and topped with syrupy peaches. However, I ran into some technical difficulties.
The first time I made the custard it would not thicken, but I realized it was because I didn't add enough cornstarch. The second time, I thought everything went well, but after sitting in the fridge overnight, the custard was soupy and liquidy. While the flavor was superb (I served it to my guests parfait style), the texture was all wrong. I've made custard successfully in the past, and honestly have no clue what went wrong.

Can you help me? Should I have let the custard boil longer? Did it need more fridge time?