Two loaves of sourdough bread:
It is made by cultivating wild yeast in a jar of flour and water, and then using it to lift the bread dough of flour and water. Some homeschoolers might be able to get away with this as an excuse to study yeast for “science class” hint hint. It also is useful for tasty and delicious sandwiches of various kinds - part of the reason the restaurant sandwich tastes better than the one you make at home.
However, I should warn folks that the Internet disagrees on how to make the bread, which types of flour and water work best, the ideal temperature for yeast cultivation, and even the indicators about when the starter is ready for baking. insert Miss_S stressing about whether or not she has cultivated enough yeast
How did our ancestors survive before commercial yeast existed? I would think that biologists would have a better way to test for the right amount of yeast and bacteria in the cultured starter which would help.
Barring that, it’s probably better to find something local to your area or just taking a recipe and rolling with it rather than getting a second, third, fifth opinion like I did, otherwise you will have cultivated an excess amount of misery.