We made four small batches of cookies consisting of 1/2 cup single ingredient peanut butter, 1/2 dark brown sugar, and 1/2 egg. The nerdlet's was the only one that varied here and that was because in her vigorous stirring she pushed some of the brown sugar out of her batch. I don't think it was really enough to make a difference here.
The girls were then allowed to choose what to add to their batch.
The drama princess chose 1/3 cup cauliflower, which I steamed and put through the food processor. They came out dark and gooey and spread the most. They were the only ones to stick to the foil. They took much longer than the other cookies to cook.
The nerdlet chose 1/3 cup chocolate chips. These retained their shape and original color the most. They required the least cooking and seemed to hold their shape the best.
Darth Baby reached for the extracts, which I interpreted to mean 1 tsp of vanilla extract. They spread very little and while they were the darkest batter, they lightened to close to the same color as those without. Sorry about the picture. I didn't bother to even look at the pictures until I let them dig into the cookies.
I chose for the bear cub and she went with 1/3 cup flour, a pinch of salt, and two pinches of baking soda. They spread and rose, lightened quite a bit from the batter, and were very crumbly.
The drama princess was sure that she would like the flour batch the most, but it turned out that she liked the chocolate chip version the most. My three girls actually liked the cauliflower version the most, which came out very gooey, but definitely retained the most peanut butter flavor. The bear cub's version with the flour, salt, and baking soda was the least peanut buttery and the least popular, but definitely came out the most like a typical cookie.
All four of the girls seemed to really enjoy this experiment and it was a great way to talk about experimental controls and test results.