What is past perfect of cook?

The past perfect of "cook" is had cooked.

Here's how it's used:

* I had cooked dinner before they arrived. (This means you finished cooking dinner before they got there.)

* She had cooked the chicken for hours, but it still wasn't done. (This implies that she spent a long time cooking the chicken.)

The past perfect tense is used to talk about an action that happened before another action in the past.