If the angle of the hole's walls is the same for the whole circumference, mount the palette on an angle jig so the walls are vertical then come in with a pocket, contour or even boring operation.
If the angle is changing or your machine won't support the Z height needed to clear the palette on the angle, look at mounting it flat on a jig that incorporates a spoil board, rough out with a straight cutter and then put the angled faces on using a spherical ball mill aka lollipop cutter.