machining a internal recess

Hello

I've got to machine a box type component about 300 x 200 x 150 size with a wall thickness of 4mm. On one wall there is a recess on the inside of 1mm. I wasn't sure what type of cutter to use was thinking of a woodruff type but not sure about the finish it would leave.

Any ideas of the best way?

Thanks in advance Mick