Given the background description of some cooking related query, summarize the question into a title

[Q]: I was making pancakes that called for melted butter in the recipe and when I added cold milk the butter re-solidified. How did that mess up the pancakes? Was the texture more dense and less fluffy? So I presume this batter could not be made ahead of time and refrigerated?
[A]: Melted butter or not for pancake batter?


[Q]: Many a recipe or package instructs: 'cook uncovered' without stating a reason. As a general matter, is this to protect me from boilover, or does it have some more subtle purpose?
[A]: When a recipe says, 'simmer uncovered', what's the issue?


[Q]: I've made roux some time ago. Forgot to put the date on the container. How long will it keep in the fridge? I'll be making a sauce in a day or two...
[A]:
How long will roux keep?