Recently, I've used a couple of recipes that call for adding melted, cooled butter to liquid ingredients, usually involving milk. Admittedly, I've not always been diligent about letting the butter cool, but even when I have, it congeals back up into, well, butter clumps.
Is there some trick to keeping the butter liquid when adding it to other liquids? Do I need to be allowing the milk to come to room temperature before adding butter? Any help is greatly appreciated.