Countersunk Screw Hole

Hi,

I am finding it difficult to make a countersunk slotted hole for a countersunk screw, I have added the 5mm slot for the screw and added a further circle at 10 mm which would be the width of the countersunk head but I cant work out how i would pull say 45 degrees from the top circle if that makes sense, any help appreciated.

Thanks Stuart