Testing Custard-Type Pies for Doneness
The most common doneness test for custard pies is to insert a table knife about an inch from the center of the pie. If it comes out clean, the pie is done, Or try the jiggle test. Gently shake the pie plate. If the center of the pie slightly jiggles, it's done. As it cools, the residual heat in the filling will finish baking the center.