Frame work attached to the wall.
I made the frame out of the driest 2×4 lumber I could find, which I jointed and surfaced to make it straight, flat, square and consistent in dimension. As you can see, I used pocket screw joinery to assemble it. I swear by the system, it is almost foolproof and very strong and perfect for this kind of installation. The frame was screwed, high up on the frame, to a horizontal framing member in the wall in eight places – it isn’t going anywhere! I glued the pre-stained underside to the frame before mounting it to the wall and as you can see, it was sized to clear the bricks. I believe this method contributed to how little flex there is when a load is placed on the mantle, pretty impressive since it is floating there at this point!