Where is the boss key in the earth temple in the legend of Zelda the wind waker

There is a tall, circular room with a spiral staircase at the end of the Earth Temple. It has one of those big teleport pots, and if you fall down to the bottom there is that cursed smoke. Directly ahead of you is the door to the boss room, you can reach it using the Deku Leaf.
If you go down the stairs (there should be a missing section) you eventually come to a door. Go through this (taking the bird-girl with you) and you'll come to a large room with more light-puzzles. At the far end of the room is one of those big faces, shine light in both it's eyes and a passage to the Big Key opens. The room is a bit of a puzzle, first you need to get bird-girl to fly only the large central area. there should be a button to press. Once she's pressed it a shutter will open allowing light into the room. You'll need to move several mirrors and dissolve some walls before you can get the light in the right place.
Once the passage is opened go through the door. This is a reasonably tough room. There is one Darknut (big guy in armour) but the real challenge are the two flying skulls. If they touch you then you can't use your sword for a few seconds. You can use the Deku Leaf to blow the skulls out of the air, they'll be paralysed and smoke-free for a little while. Once you've dealt with the skulls the Darknut can be fought in the usual way (parrying when he has a sword). Once you've cleared the room of enemies you can open the chest with the Big Key in it. Leave the room by the way you came and go through the room with the mirrors to get back to the room you started in.