Typically, an egg wash is applied to the top of a pie crust before it's baked to achieve a golden, slightly glossy finish. However, for par-baked or blind-baked pie crusts, the timing for the egg wash is different. In these cases, the egg wash acts as a sealant to prevent wet fillings like custards and puddings from seeping into the crust. Therefore, it's best to apply the egg wash after the crust has been par-baked, just before it goes back into the oven for its final bake.