Question

Which rule would help you punctuate the bold portion of this sentence correctly? “I will prepare an excellent meal for you said the cook.

Answer 1

you have to put quotation marks at the beginning and the end of the sentence when some one says something...

"I will prepare an excellent meal for you" said the cook.

What the cook says is direct speech, so it should be with quotation marks.
Not for indirect speech : the cook said he will prepare an excellent meal for him (me).

Answer 2

There is no bold portion in the sentence you gave
I would add some kind of punctuation between you and said.
I will prepare an excellent meal for you. Said the cook.