I've mentioned this in a few topics where people are having trouble with the butler cooking 2 times per hour, but because the reactions are still full of surprise I decided to make a separate topic for this, so anyone will know.
The butler is a fine person, really, but you just have to guide the good man a little bit.
So if you are having a kitchen with a door all you need to do is
locking that door from the butler. That's all, easy as that. But because it's so easy, people may think about a solution in a more difficult way. See, not necessary.
Have fun with your staff!