Allow me to completely over analyze this now.
First off, from the feeling inside a car on a hot summer day, I have no doubt that you COULD cook some things inside a car. After all, the lowest setting on your oven is 140 degrees. How hot it actually gets inside a car, I do not know. But for the sake of argument, let’s say it does get hot enough to turn dough into cookies. I’m not sure it would work, I mean you do need to sort of carmelize those sugars to get your cookies brown and of a consistent texture, I’m not sure if a car could do that, because if it could get hot enough to do that, would we even be able to get into our cars in the summer? I guess I don’t know quite enough about the chemistry of baking and the maximum air temp which can be achieved by a car to answer this definitively.
The first problem I would see however is how hot is it outside, and what relationship does the car interior bear to the exterior air temp, and the amount of direct sunlight? Is there a max temp? Does it vary from car to car…like would a Hyundai Sonata and a Subaru Outback given the same air temp and direct sun percentage achieve the same internal car air temp at the same time? And what about the color of the car? We all know that a dark color will absorb more of the sun’s rays than a light color, so would that lead to achieving an even higher internal temp, or would it only cause the max internal temp (assuming there is such a thing) to be achieved more quickly.
I would content that baking times could vary widely, and you may not achieve a consistent product depending on a number of factors, from the size, shape, make, model and color of your car, to the air temp, the percentage of direct sunlight and possibly even the angle of the sun which would vary with your personal geographic location. And would there be any circumstances, or would all cars given a certain temp achieve a high enough temp to achieve what we know as “baking” as opposed to simply “warming”?
Another thing about food is the texture and indeed the flavor. Some things beg to be cooked slowly…certain meats achieve a fall off the bone tenderness with a lower cooking temp at a longer duration. Some foods however taste better if they are cooked at higher temps. Know why you can’t make a homemade pizza as good as your favorite pizza joint? Because their ovens are more intense. French fries taste way better if the oil is REALLY hot than if it’s just hot enough. Even cookies, you cook them at a higher temp vs. a lower temp, I suspect you will see a difference between soft, gooey cookies, and crispy, dunkable cookies. Not sure which way results in the best.
But having said all that, I’ll say it’s worth a try. After all, if you bring home a pizza in your car, your car smells like pizza for a couple days….I imagine your car would smell like fresh baked cookies for a couple days after this experiment, even if it failed, and that can’t be a bad thing.
I think however I would use pasteurized eggs, just in case.