Is it okay to cook multiple pies at one time? For example, if I make enough batter for two sweet potato pies or two pecan pies, can I cook both of them at the same time? If so, how would I vary the cooking time or temperature? I'm asking because the recipe always states, "...place the pie in the center of the oven." Obviously this would be impossible if baking two pies on the same oven rack.
Oh, we love questions that are easy to answer just go out and buy a convection oven, the kind that has a fan and an additional heating element to evenly circulate the air in your oven so that it has a consistent temperature from front to back, side to side, and top to bottom. No? Not prepared to make that kind of commitment for a couple of pecan pies?
The problem is that the temperature in a conventional oven is not consistent. Even without a convection oven, your pie cooks primarily by convection that is, the air in the oven is heated, flows around in the oven, and transfers heat to the pie. The temperature in the middle of the oven has the best chance of offering the most consistent temperature, which is why all those recipes specify it.
You certainly can cook two pies at once, but you have to be more attentive and take steps to help them cook evenly. You want to disrupt the natural flow of air in the oven as little as possible. That's why cookie recipes often tell you to keep the baking sheets as many inches as possible from the sides of the oven they're so big, they block a lot of the air flow.
We often put two pies or cakes on the same oven rack. We stagger them so one is toward the back and side and the other toward the front and the other side. Halfway through the cooking time, we switch them and rotate them a half turn, so that the edges that were close to the side and back are now somewhere in the center of the oven. If we cook two pies on separate oven racks, we also have them staggered so that the one on the bottom doesn't block much of the heat from reaching the top one. And halfway through, we move the bottom one to the top and the top one to the bottom, and rotate them, as well.
It will not take much longer to cook one pie than two. But they may not cook evenly, so you have to keep watch and rescue each as it is done, even if one takes 5 minutes longer than its mate.