First, forget everything you’ve heard about a clean knife. That works for cakes. Not for custard pies. Please don’t stick a knife in there.
You want the pie to look like Jell-O on a trampoline. No, really. When you gently nudge the pan, the center should jiggle—but it should jiggle like a single, unified mass.
Think of it as a sheet of jelly, not a liquid wave. If it ripples like soup, it’s underdone. If it’s completely still? Overdone. You want that soft, quivery wobble in the absolute center.
The 2-Inch Ring of Confidence
Here’s a pro tip that changed my pie life. The edges of the pie should be set and firm. Look for a ring about two inches around the outer crust.
That ring should look puffed and solid, maybe even slightly cracked. But the middle? That middle inch or two should still have that gentle jiggle.
Why? Because of carryover cooking. That pie will keep baking on your counter for another 15 minutes. You pull it out when it’s almost done, not totally done.