If a cookie is baked with the correct time and temperature but turns out dry and hard, what likely happened?

When a cookie is baked properly but ends up dry and hard, the most likely reason is an imbalance in the ingredient proportions. Too much flour can absorb too much moisture, leading to a dense and dry texture. Cookies rely on the right amount of flour to maintain their structure while still being tender.

If there is too little egg, the cookie may not bind properly or have enough richness, but it is less likely to result in a dry cookie compared to excess flour. Sugar, on the other hand, contributes moisture and can help create a tender texture by preventing the cookie from becoming too hard. Therefore, too much sugar would not typically lead to dryness.

Insufficient baking powder would affect the rise of the cookies and could lead to them being dense, but it does not directly cause dryness. Thus, excessive flour is the best explanation for why the cookie emerged dry and hard after baking, aligning with the need for careful measurement of ingredients in baking.