Originally Posted by Speedy Petey
How about a round Wiremold box painted to match either the wood color or the fixture color. This way it will look like part of the fixture as opposed to just a box.
You can come into the back of the WM box with an NM connector.
I second that suggestion. Round Wiremold boxes are available in many diameters at the electrical supply house. I'm certain that you'll be able to get one the same diameter as the canopy of the chandelier. This way, to the untrained eye, the box will not be at all notciable. Especially if you paint it to match the wood or the fixture, as Speedy suggests. The other option is to recess a 1/2" deep "pancake box" into the beam if the beam is decorative. If the beam is structural, don't do that.